perf: use simdutf8 to validate UTF-8 when reading files

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #237 will not alter performance

_{Comparing simd (4cad9e6) with main (6c4297b)}

Summary

✅ 3 untouched benchmarks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 71.42857% with 4 lines in your changes missing coverage. Please review.

Project coverage is 96.88%. Comparing base (6c4297b) to head (4cad9e6). Report is 1 commits behind head on main.

Files	Patch %	Lines
src/file_system.rs	71.42%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #237 +/- ## ========================================== - Coverage 97.04% 96.88% -0.16% ========================================== Files 11 11 Lines 2366 2377 +11 ========================================== + Hits 2296 2303 +7 - Misses 70 74 +4 ```

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