refactor: record URL mappings during parsing

[luojiyin1987]

Summary

• Record resource and definition URL segments from parser events.
• Keep existing empty URL boundary handling.
• Keep autolink URL mappings unavailable.
• Remove the post-parse URL scanner and its span state.
• Keep the URL benchmark on the production parse path.

This removes duplicate URL parsing and decoding.
It also reduces duplicated parser semantics.

Validation

• pnpm test: 1978 tests passed.
• pnpm run lint passed.
• pnpm run build passed.
• node scripts/bench-source-map.mjs --smoke passed.
• node scripts/bench-parse.mjs --smoke passed with AST parity.

Benchmark

GitHub CI measured 696.31 ms for the 512 KiB URL case.
The CI growth ratio was 3.97x from 128 KiB to 512 KiB.
This keeps near-linear growth without a wall-time regression.

A local run measured 461.69 ms and a 3.61x growth ratio.