fix(return): error if return used outside sourced script or function

[reubeno]

Resolves a TODO in the implementation of the return built-in to check for current function or sourced script. To do this, required tracking the distinction between a top-level executed script vs. a script sourced via source or ..

Adds some compat test cases too for these return uses, refactoring them out of the general function part of the test suite.

Resolves #338 (the rest of it not covered by previous fixes).

[github-actions]

Test Results

    3 files     14 suites   5m 33s ⏱️
  621 tests   621 ✅ 0 💤 0 ❌
1 849 runs  1 849 ✅ 0 💤 0 ❌

Results for commit 2b5bb75.

♻️ This comment has been updated with latest results.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	16.27 μs	16.18 μs	-0.09 μs	⚪ Unchanged
eval_arithmetic	0.20 μs	0.19 μs	-0.01 μs	🟢 -5.10%
expand_one_string	1.56 μs	1.53 μs	-0.03 μs	⚪ Unchanged
for_loop	32.46 μs	32.32 μs	-0.15 μs	⚪ Unchanged
function_call	3.33 μs	3.22 μs	-0.10 μs	⚪ Unchanged
instantiate_shell	49.06 μs	48.48 μs	-0.58 μs	🟢 -1.18%
instantiate_shell_with_init_scripts	21901.43 μs	21930.72 μs	29.29 μs	⚪ Unchanged
parse_bash_completion	1676.56 μs	1662.56 μs	-14.00 μs	⚪ Unchanged
parse_sample_script	1.81 μs	1.76 μs	-0.05 μs	🟢 -2.87%
run_echo_builtin_command	16.53 μs	16.27 μs	-0.26 μs	⚪ Unchanged
run_one_external_command	4210.64 μs	2134.44 μs	-2076.20 μs	🟢 -49.31%
tokenize_sample_script	2.78 μs	2.79 μs	0.01 μs	🟠 +0.47%

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/builtins/dot.rs	🟢 91.67%	🟢 95.83%	🟢 4.16%
brush-core/src/builtins/return_.rs	🟢 81.82%	🟢 100%	🟢 18.18%
brush-core/src/shell.rs	🟢 77.62%	🟢 78.34%	🟢 0.72%
Overall Coverage	🟢 74.7%	🟢 74.77%	🟢 0.07%

Minimum allowed coverage is 70%, this run produced 74.77%