Refactor generator

[TimothyMakkison]

• Change List usage to array
• Reduce intermediary collection creation

Benchmarks - timing is inaccurate, I wanted to see memory usage

Before

Method	Mean	Error	StdDev	Median	Gen0	Gen1	Allocated
RunGenerator	162.5 ms	6.15 ms	16.95 ms	155.1 ms	10000.0000	4000.0000	97.02 MB

After

Method	Mean	Error	StdDev	Median	Gen0	Gen1	Allocated
RunGenerator	166.1 ms	6.86 ms	20.00 ms	155.8 ms	10000.0000	4000.0000	96.53 MB

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

This is a solid refactoring PR that aligns well with TUnit's performance-first philosophy. The changes reduce memory allocations by approximately 490KB through systematic optimization of collection usage in the source generator. The refactoring includes:

• Converting List to arrays where appropriate
• Eliminating unnecessary intermediate collection materializations
• Removing unused method parameters (cleaner API surface)
• Modernizing code with switch expressions and pattern matching
• Improving category deduplication with HashSet

All changes are mechanical refactorings with no behavioral differences. The benchmark results demonstrate measurable performance improvements (97.02 MB to 96.53 MB allocated).