Harden path parser

[CathalMullan]

Fuzzer doesn't immediately fail anymore, so we'll call that a win.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #104 will degrade performances by 7.53%

_{Comparing 103-harden-path-parser (7eb3a1d) with main (4f420d8)}

Summary

❌ 1 (👁 1) regressions ✅ 21 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	103-harden-path-parser	Change
👁	matchit benchmarks/gonzales	4.7 µs	5 µs	-7.53%