Kill lib.rs CLI escapes via function and mutator slices (#69)

[jonbaldie]

Summary

Closes #69 (child of #40).

Measures every CLI entry function in src/lib.rs using memory-safe, function-scoped and mutator-group batches (--workers 1, CARGO_BUILD_JOBS=1, narrow tests --test-flags "--test cli --lib" without --coverage). Kills escaped mutants via integration tests through messrust::run in tests/cli.rs.

Batch Measurement Results

Environment: Docker container capped at 2 CPUs / 4 GB RAM, CARGO_BUILD_JOBS=1, --workers 1, --test-flags "--test cli --lib", temporary directories under $TMPDIR/mutarust-* removed after each batch.

Function	Mutants	Killed	Escaped	Errored	Skipped	MSI
handle_info_flags	4	1	0	0	3	100.00%
print_usage	0	0	0	0	0	N/A
parse_priority	6	6	0	0	0	100.00%
source_suffixes	2	0	0	0	2	100.00%
suffix_list	2	0	0	0	2	100.00%
split_list	0	0	0	0	0	N/A
required_value	0	0	0	0	0	N/A
apply_flag_option	13	13	0	0	0	100.00%
apply_value_option	11	11	0	0	0	100.00%
prepare_analysis	1	1	0	0	0	100.00%
run_analysis	10	6	0	0	4	100.00%
parse_args (all mutator groups)	32	29	0	2	1	100.00%
run	32	26	2	0	4	93.75%
default (Options)	4	2	1	0	1	75.00%

Escaped Mutants and Equivalence Notes

Across all CLI entry functions, 3 escaped mutants remain, and all 3 are proven behaviorally equivalent:

1. src/lib.rs:90 in run:
   return EXIT_SUCCESS; -> return 0; (statement/return)
   Equivalence note: EXIT_SUCCESS is pub const EXIT_SUCCESS: i32 = 0;. Returning literal 0 produces identical behavior.

2. src/lib.rs:95 in run:
   return code; -> return 0; (statement/return)
   Equivalence note: handle_info_flags returns Some(EXIT_SUCCESS) (which is 0) on info flags (--version, --help, -h), and None otherwise. When code is returned, its value is always 0. Returning literal 0 produces identical behavior.

3. src/lib.rs:72 in default:
   max_priority: 1 -> max_priority: 0; (composite/field-clear)
   Equivalence note: Rule priorities are integers in range 1..=5. Rules are filtered by max priority when opts.max_priority > 0 && priority < opts.max_priority. If max_priority == 1, priority < 1 is false for all rules (since priority >= 1). If max_priority == 0, opts.max_priority > 0 is false. Both conditions filter zero rules. Behavior is identical.

The fourth mutant, max_priority: 1 -> max_priority: 2 (numbers/incrementer), escaped previously. It is killed by the new test default_maximumpriority_includes_priority_one_rules in tests/cli.rs (testing cleancode ruleset containing BooleanArgumentFlag with priority 1).

Changes

• tests/cli.rs: Add integration test default_maximumpriority_includes_priority_one_rules through messrust::run.