fix: bang formatted without space leads to invalid command

[cilki]

When formatting a negated command like:

! $0

Pipeline::fmt results in:

!$0

which is incorrect.

[reubeno]

Thanks for the contribution! The change seems reasonable.

I’ve queued the PR checks to run so we can see their results.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	17.35 μs	17.54 μs	0.19 μs	🟠 +1.08%
eval_arithmetic	0.16 μs	0.16 μs	-0.00 μs	⚪ Unchanged
expand_one_string	1.57 μs	1.60 μs	0.02 μs	⚪ Unchanged
for_loop	31.09 μs	30.68 μs	-0.42 μs	⚪ Unchanged
full_peg_complex	57.32 μs	57.12 μs	-0.21 μs	⚪ Unchanged
full_peg_for_loop	6.37 μs	6.29 μs	-0.08 μs	⚪ Unchanged
full_peg_nested_expansions	16.54 μs	16.78 μs	0.24 μs	🟠 +1.46%
full_peg_pipeline	4.20 μs	4.23 μs	0.02 μs	⚪ Unchanged
full_peg_simple	1.72 μs	1.78 μs	0.06 μs	🟠 +3.48%
function_call	4.23 μs	3.56 μs	-0.67 μs	🟢 -15.78%
instantiate_shell	55.63 μs	55.39 μs	-0.24 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	30697.73 μs	30868.43 μs	170.70 μs	⚪ Unchanged
parse_peg_bash_completion	2093.14 μs	2091.08 μs	-2.06 μs	⚪ Unchanged
parse_peg_complex	19.01 μs	18.05 μs	-0.96 μs	🟢 -5.05%
parse_peg_for_loop	1.90 μs	1.87 μs	-0.03 μs	🟢 -1.74%
parse_peg_pipeline	1.91 μs	2.03 μs	0.12 μs	⚪ Unchanged
parse_peg_simple	1.03 μs	1.06 μs	0.03 μs	🟠 +3.02%
run_echo_builtin_command	17.35 μs	16.69 μs	-0.66 μs	🟢 -3.81%
tokenize_sample_script	3.58 μs	3.60 μs	0.02 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-test-harness/src/comparison.rs	🟢 76.92%	🟢 80.77%	🟢 3.85%
brush-test-harness/src/reporting.rs	🔴 11.62%	🔴 29.93%	🟢 18.31%
brush-test-harness/src/runner.rs	🟢 84.17%	🟢 84.77%	🟢 0.6%
brush-test-harness/src/util.rs	🔴 47.76%	🟠 71.64%	🟢 23.88%
Overall Coverage	🟢 74.39%	🟢 74.72%	🟢 0.33%

Minimum allowed coverage is 70%, this run produced 74.72%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1582	75.01
❗️ Error	17	0.81
❌ Fail	156	7.40
⏩ Skip	339	16.07
❎ Expected Fail	13	0.62
✔️ Unexpected Pass	2	0.09
📊 Total	2109	100.00

[reubeno]

The failing PR checks are unrelated; we'll resolve those separately.

Change looks good.