Clarify passing ValueT to scan_by_key tuning

[bernhardmgruber]

This PR clarifies that passing ValueT is to the tunings is correct.

See also discussion here: #3139 (comment)

[github-actions]

🟩 CI finished in 1h 53m: Pass: 100%/94 | Total: 2d 13h | Avg: 39m 15s | Max: 1h 08m | Hits: 74%/12324

• 🟩 thrust: Pass: 100%/46 | Total: 1d 00h | Avg: 31m 40s | Max: 59m 54s | Hits: 76%/9260

  🟩 cmake_options
    🟩 -DTHRUST_DISPATCH_TYPE=Force32bit Pass: 100%/2   | Total: 45m 49s | Avg: 22m 54s | Max: 29m 47s
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  🟩 ctk
    🟩 11.1               Pass: 100%/7   | Total:  3h 21m | Avg: 28m 45s | Max: 50m 55s | Hits:  71%/1852  
    🟩 12.5               Pass: 100%/2   | Total:  1h 45m | Avg: 52m 56s | Max: 55m 34s
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    🟩 ClangCUDA18        Pass: 100%/2   | Total: 55m 17s | Avg: 27m 38s | Max: 29m 16s
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    🟩 ClangCUDA          Pass: 100%/2   | Total: 55m 17s | Avg: 27m 38s | Max: 29m 16s
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    🟩 Clang11            Pass: 100%/1   | Total: 30m 45s | Avg: 30m 45s | Max: 30m 45s
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    🟩 MSVC14.29          Pass: 100%/1   | Total: 59m 54s | Avg: 59m 54s | Max: 59m 54s | Hits:  71%/1852  
    🟩 MSVC14.39          Pass: 100%/3   | Total:  2h 11m | Avg: 43m 57s | Max: 57m 43s | Hits:  80%/5556  
    🟩 NVHPC24.7          Pass: 100%/2   | Total:  1h 45m | Avg: 52m 56s | Max: 55m 34s
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    🟩 Clang              Pass: 100%/19  | Total:  8h 53m | Avg: 28m 06s | Max: 33m 52s
    🟩 GCC                Pass: 100%/19  | Total:  8h 51m | Avg: 27m 57s | Max: 43m 36s
    🟩 Intel              Pass: 100%/1   | Total: 43m 09s | Avg: 43m 09s | Max: 43m 09s
    🟩 MSVC               Pass: 100%/5   | Total:  4h 02m | Avg: 48m 32s | Max: 59m 54s | Hits:  76%/9260  
    🟩 NVHPC              Pass: 100%/2   | Total:  1h 45m | Avg: 52m 56s | Max: 55m 34s
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    🟩 v100               Pass: 100%/46  | Total:  1d 00h | Avg: 31m 40s | Max: 59m 54s | Hits:  76%/9260  
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    🟩 Build              Pass: 100%/40  | Total: 22h 47m | Avg: 34m 11s | Max: 59m 54s | Hits:  71%/7408  
    🟩 TestCPU            Pass: 100%/3   | Total: 37m 20s | Avg: 12m 26s | Max: 22m 32s | Hits:  99%/1852  
    🟩 TestGPU            Pass: 100%/3   | Total: 51m 54s | Avg: 17m 18s | Max: 18m 50s
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• 🟩 cub: Pass: 100%/45 | Total: 1d 12h | Avg: 48m 40s | Max: 1h 08m | Hits: 65%/3064

  🟩 cpu
    🟩 amd64              Pass: 100%/43  | Total:  1d 10h | Avg: 48m 20s | Max:  1h 08m | Hits:  65%/3064  
    🟩 arm64              Pass: 100%/2   | Total:  1h 52m | Avg: 56m 02s | Max: 56m 05s
  🟩 ctk
    🟩 11.1               Pass: 100%/7   | Total:  5h 27m | Avg: 46m 48s | Max: 57m 14s | Hits:  65%/766   
    🟩 12.5               Pass: 100%/2   | Total:  2h 09m | Avg:  1h 04m | Max:  1h 08m
    🟩 12.6               Pass: 100%/36  | Total:  1d 04h | Avg: 48m 08s | Max:  1h 05m | Hits:  65%/2298  
  🟩 cudacxx
    🟩 ClangCUDA18        Pass: 100%/2   | Total:  1h 54m | Avg: 57m 14s | Max: 57m 38s
    🟩 nvcc11.1           Pass: 100%/7   | Total:  5h 27m | Avg: 46m 48s | Max: 57m 14s | Hits:  65%/766   
    🟩 nvcc12.5           Pass: 100%/2   | Total:  2h 09m | Avg:  1h 04m | Max:  1h 08m
    🟩 nvcc12.6           Pass: 100%/34  | Total:  1d 02h | Avg: 47m 36s | Max:  1h 05m | Hits:  65%/2298  
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    🟩 ClangCUDA          Pass: 100%/2   | Total:  1h 54m | Avg: 57m 14s | Max: 57m 38s
    🟩 nvcc               Pass: 100%/43  | Total:  1d 10h | Avg: 48m 16s | Max:  1h 08m | Hits:  65%/3064  
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    🟩 Clang9             Pass: 100%/4   | Total:  3h 12m | Avg: 48m 01s | Max: 51m 38s
    🟩 Clang10            Pass: 100%/1   | Total: 52m 35s | Avg: 52m 35s | Max: 52m 35s
    🟩 Clang11            Pass: 100%/1   | Total: 53m 42s | Avg: 53m 42s | Max: 53m 42s
    🟩 Clang12            Pass: 100%/1   | Total: 50m 57s | Avg: 50m 57s | Max: 50m 57s
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    🟩 Clang14            Pass: 100%/1   | Total: 58m 00s | Avg: 58m 00s | Max: 58m 00s
    🟩 Clang15            Pass: 100%/1   | Total: 51m 15s | Avg: 51m 15s | Max: 51m 15s
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    🟩 Clang18            Pass: 100%/7   | Total:  5h 32m | Avg: 47m 32s | Max: 57m 38s
    🟩 GCC6               Pass: 100%/2   | Total:  1h 32m | Avg: 46m 05s | Max: 46m 20s
    🟩 GCC7               Pass: 100%/2   | Total:  1h 45m | Avg: 52m 39s | Max: 54m 00s
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    🟩 Intel2023.2.0      Pass: 100%/1   | Total: 55m 34s | Avg: 55m 34s | Max: 55m 34s
    🟩 MSVC14.16          Pass: 100%/1   | Total: 57m 14s | Avg: 57m 14s | Max: 57m 14s | Hits:  65%/766   
    🟩 MSVC14.29          Pass: 100%/1   | Total:  1h 04m | Avg:  1h 04m | Max:  1h 04m | Hits:  65%/766   
    🟩 MSVC14.39          Pass: 100%/2   | Total:  2h 03m | Avg:  1h 01m | Max:  1h 05m | Hits:  65%/1532  
    🟩 NVHPC24.7          Pass: 100%/2   | Total:  2h 09m | Avg:  1h 04m | Max:  1h 08m
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    🟩 Clang              Pass: 100%/19  | Total: 15h 46m | Avg: 49m 47s | Max: 58m 00s
    🟩 GCC                Pass: 100%/19  | Total: 13h 33m | Avg: 42m 49s | Max: 56m 00s
    🟩 Intel              Pass: 100%/1   | Total: 55m 34s | Avg: 55m 34s | Max: 55m 34s
    🟩 MSVC               Pass: 100%/4   | Total:  4h 05m | Avg:  1h 01m | Max:  1h 05m | Hits:  65%/3064  
    🟩 NVHPC              Pass: 100%/2   | Total:  2h 09m | Avg:  1h 04m | Max:  1h 08m
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    🟩 v100               Pass: 100%/45  | Total:  1d 12h | Avg: 48m 40s | Max:  1h 08m | Hits:  65%/3064  
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    🟩 Build              Pass: 100%/39  | Total:  1d 10h | Avg: 52m 42s | Max:  1h 08m | Hits:  65%/3064  
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    🟩 TestGPU            Pass: 100%/2   | Total: 43m 46s | Avg: 21m 53s | Max: 22m 14s
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    🟩 90a                Pass: 100%/1   | Total: 22m 38s | Avg: 22m 38s | Max: 22m 38s
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    🟩 11                 Pass: 100%/5   | Total:  3h 59m | Avg: 47m 49s | Max: 51m 38s
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• 🟩 cccl_c_parallel: Pass: 100%/2 | Total: 9m 00s | Avg: 4m 30s | Max: 6m 55s

  🟩 cpu
    🟩 amd64              Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
  🟩 ctk
    🟩 12.6               Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
  🟩 cudacxx
    🟩 nvcc12.6           Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
  🟩 cudacxx_family
    🟩 nvcc               Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
  🟩 cxx
    🟩 GCC13              Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
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    🟩 GCC                Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
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    🟩 v100               Pass: 100%/2   | Total:  9m 00s | Avg:  4m 30s | Max:  6m 55s
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    🟩 Test               Pass: 100%/1   | Total:  6m 55s | Avg:  6m 55s | Max:  6m 55s
  

• 🟩 python: Pass: 100%/1 | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s

  🟩 cpu
    🟩 amd64              Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  🟩 ctk
    🟩 12.6               Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  🟩 cudacxx
    🟩 nvcc12.6           Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  🟩 cudacxx_family
    🟩 nvcc               Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  🟩 cxx
    🟩 GCC13              Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
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    🟩 GCC                Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
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    🟩 v100               Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  🟩 jobs
    🟩 Test               Pass: 100%/1   | Total: 33m 59s | Avg: 33m 59s | Max: 33m 59s
  

👃 Inspect Changes

Modifications in project?

	Project
	CCCL Infrastructure
	libcu++
+/-	CUB
	Thrust
	CUDA Experimental
	python
	CCCL C Parallel Library
	Catch2Helper

Modifications in project or dependencies?

	Project
	CCCL Infrastructure
	libcu++
+/-	CUB
+/-	Thrust
	CUDA Experimental
+/-	python
+/-	CCCL C Parallel Library
+/-	Catch2Helper

🏃‍ Runner counts (total jobs: 94)

#	Runner
70	linux-amd64-cpu16
11	linux-amd64-gpu-v100-latest-1
9	windows-amd64-cpu16
4	linux-arm64-cpu16