fix: leave trailing whitespace out of reedline completion suggestions

[reubeno]

In the future we can simplify this (rather than having to postprocess the candidates), but this is a more targeted fix that works for now without a bit of refactoring.

[github-actions]

Test Results

  2 files    9 suites   1m 2s ⏱️
478 tests 478 ✅ 0 💤 0 ❌
947 runs  947 ✅ 0 💤 0 ❌

Results for commit d66702f.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
expand_one_string	3.42 μs	3.42 μs	0.00 μs	⚪ Unchanged
instantiate_shell	60.08 μs	59.78 μs	-0.30 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	27915.57 μs	28678.17 μs	762.60 μs	🟠 +2.73%
parse_bash_completion	2699.80 μs	2727.75 μs	27.95 μs	⚪ Unchanged
parse_sample_script	3.99 μs	4.08 μs	0.09 μs	🟠 +2.36%
run_echo_builtin_command	91.19 μs	89.78 μs	-1.41 μs	⚪ Unchanged
run_one_builtin_command	108.10 μs	107.99 μs	-0.11 μs	⚪ Unchanged
run_one_external_command	1968.60 μs	2059.99 μs	91.40 μs	🟠 +4.64%
run_one_external_command_directly	1005.46 μs	1013.99 μs	8.54 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/shell.rs	🟢 78.4%	🟢 78.54%	🟢 0.14%
Overall Coverage	🟢 72.67%	🟢 72.66%	🔴 -0.01%

Minimum allowed coverage is 70%, this run produced 72.66%