fix: do not invoke debug traps during completion funcs

[reubeno]

Not the best implementation, but this seems to match what bash does and can speed up completion when using debug traps (such as the one that starship installs).

[github-actions]

Test Results

410 tests   396 ✅  21s ⏱️
 68 suites   14 💤
 11 files      0 ❌

Results for commit 1587bd5.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
expand_one_string	3.60 μs	3.60 μs	-0.00 μs	⚪ Unchanged
instantiate_shell	60.16 μs	60.38 μs	0.22 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	27943.91 μs	27389.76 μs	-554.14 μs	🟢 -1.98%
parse_bash_completion	5541.92 μs	5577.60 μs	35.68 μs	🟠 +0.64%
parse_sample_script	8.79 μs	8.86 μs	0.07 μs	🟠 +0.83%
run_echo_builtin_command	94.73 μs	93.01 μs	-1.72 μs	🟢 -1.82%
run_one_builtin_command	114.24 μs	111.85 μs	-2.39 μs	🟢 -2.09%
run_one_external_command	1939.63 μs	1945.86 μs	6.23 μs	⚪ Unchanged
run_one_external_command_directly	999.22 μs	993.70 μs	-5.52 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/completion.rs	🔴 42.92%	🔴 42.64%	🔴 -0.28%
brush-core/src/shell.rs	🟢 78.21%	🟢 77.59%	🔴 -0.62%
brush-shell/src/main.rs	🟢 89.6%	🟢 88.8%	🔴 -0.8%
Overall Coverage	🟢 76.27%	🟢 76.21%	🔴 -0.06%

Minimum allowed coverage is 70%, this run produced 76.21%