Add missing unit tests for # noqa:-like cases

[InSyncWithFoo]

Summary

Follow-up to #16483.

This case is explicitly described in the specification, but it is not covered by any tests:

We expect a list of rule codes, separated by commas or whitespace. After splitting first on commas, and then on whitespace, we attempt to parse each item in turn. If parsing a nonempty item returns no rule codes, we stop. If no codes were found at all we warn the user with MissingCodes.

Test Plan

Unit tests.

[codspeed-hq]

CodSpeed Performance Report

Merging #16659 will degrade performances by 10.81%

_{Comparing InSyncWithFoo:noqa (7e7add7) with micha/ruff-0.10 (b8f1284)}

Summary

❌ 1 regressions
✅ 31 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	red_knot_check_file[incremental]	4.9 ms	5.5 ms	-10.81%

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[dylwil3]

Thanks! Glad they passed 😄