Inline small identifier and span helpers

[fyrsta7]

Summary

This adds #[inline] to two very small helper methods: Word::to_ident and TokenWithSpan::at.

Why this can improve performance

Both helpers are small wrapper-style methods used while constructing identifiers and token spans. Marking them inline gives the optimizer more room to remove call overhead on parser/tokenizer paths that call these helpers frequently.

Validation

• git diff --check
• cargo check

Benchmark

Current machine, release microbenchmark, 9 samples, median:

Benchmark	Base	This change	Delta
1024 identifier/span helper calls	42,798.232 ns	38,391.700 ns	10.30% faster