Optimize position tracking performance

[darthmaim]

• Move offset out of loop body
• Add fast path for \n
• Add fast path for no line breaks

The fast paths should in theory handle all cases the parser currently supports, but for correctness and future additions the advance algorithm falls back to the simple loop over all characters if the fast paths are not hit.

[Copilot]

Pull request overview

Improves parser position tracking performance by optimizing how the cursor advances through consumed input, and updates benchmarks/tooling to measure the impact.

Changes:

• Optimize advance() in packages/parser/src/cursor.ts with fast paths for '\n' and strings without line breaks, and move offset updates out of the per-character loop.
• Update the parser benchmark input to include frequent newlines to better exercise newline handling.
• Add a root bench script and a changeset for a patch release of @gw2/markup-parser.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/parser/test/parser.bench.ts	Adjust benchmark input to include \n separators for newline-heavy parsing scenarios.
packages/parser/src/cursor.ts	Add fast paths and restructure cursor advancement to reduce per-character overhead.
package.json	Add a root bench script to run workspace benchmarks.
.changeset/small-geese-refuse.md	Declare a patch release for the parser performance change.

Comments suppressed due to low confidence (1)

packages/parser/src/cursor.ts:39

• When value contains a newline, this does two passes over the string (includes('\n') and then the full character loop). If multiline chunks are possible, consider folding the newline detection into the loop (or using indexOf/lastIndexOf to jump directly) to avoid scanning from the start twice.

  // fast path for no line breaks (this is the most common case)
  if (!value.includes('\n')) {
    start.column += value.length;
    return;
  }

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