perf(parser): faster offset calculation

[overlookmotel]

A faster way to calculate offset in the lexer.

This only moves the needle because it's on the hottest path in the lexer - Lexer::offset is called for every token in Lexer::read_next_token.

[codspeed-hq]

CodSpeed Performance Report

Merging #2215 will not alter performance

_{Comparing overlookmotel:lexer-skip-offset-calc (5c9311b) with main (872d751)}

Summary

✅ 17 untouched benchmarks

[Boshen]

[Boshen]

@overlookmotel This is hard to understand without context, can you add some inline comments regarding why this is better than the previous version?

Something like:

// This is changed from self.source.len() - self.current.chars.as_str().len(),
// where ... (bunch of assembly instructions)

[overlookmotel]

Yes sure. Have added a new commit with a comment.