[Bug fix] Fix rule B909's panic when checking large loop blocks

[Embers-of-the-Fire]

Summary

This pr should close #11771 by changing LoopMutationsVisitor::<field>branch from u8 to u32.

Test Plan

Tested using the example programme mentioned in the related issue.

[codspeed-hq]

CodSpeed Performance Report

Merging #11772 will improve performances by 4.67%

_{Comparing Embers-of-the-Fire:main (06e69e0) with main (6c1fa1d)}

Summary

⚡ 1 improvements
✅ 29 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	Embers-of-the-Fire:main	Change
⚡	linter/all-with-preview-rules[numpy/globals.py]	839.1 µs	801.7 µs	+4.67%

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

Thanks