Add CodSpeed performance benchmarks for the MPD parser

[codspeed-hq]

Summary

This PR sets up continuous performance measurement with CodSpeed for dash.js.

It adds a benchmark suite targeting Dash.dependencies.DashParser — the component that turns a raw MPEG-DASH manifest (an XML string) into the JavaScript object tree the player consumes. Parsing runs on every manifest load and every live-manifest refresh, so it is a hot, CPU-bound path and a meaningful target for regression tracking.

What was added

• benchmarks/ — an isolated benchmark package with its own package.json. It is deliberately kept separate from the root project so the benchmarks can run on a modern Node.js toolchain (vitest) without pulling in the legacy, browser-only build tooling (grunt/jasmine/phantomjs) that no longer installs cleanly on current Node versions.
  • dashParser.bench.js — four benchmarks covering SegmentTemplate-based and SegmentList-based manifests at small and large sizes.
  • loadDash.js — loads the real, unmodified parser source (DashParser, X2JS, ObjectIron, Q) into a Node.js vm context and provides a browser-like environment (window.DOMParser via @xmldom/xmldom), so the benchmarks exercise the actual production code.
  • fixtures.js — generates representative manifests of varying sizes.
  • vitest.config.js — wires in @codspeed/vitest-plugin.
  • README.md — documents the setup and how to run it.
• .github/workflows/codspeed.yml — runs the benchmarks on CodSpeed in simulation mode on pushes to master, on pull requests, and via manual dispatch. It uses OIDC authentication (id-token: write) and the latest CodSpeedHQ/action@v4.
• README badge and a Benchmarks section describing how to run the suite locally.

Local verification

The suite was verified locally with the CodSpeed CLI in simulation mode. All four benchmarks are measured and results upload successfully:

Benchmark	Time
SegmentList manifest (300 segments/representation)	~212 ms
SegmentList manifest (60 segments/representation)	~39 ms
SegmentTemplate manifest (50 representations)	~11 ms
SegmentTemplate manifest (small)	~3.7 ms

Running locally

cd benchmarks
npm install
npm run bench

Next steps

• Merge to start tracking parser performance on every PR.
• Extend coverage to other hot paths (for example segment index handling) as needed.

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 4 new benchmarks were detected.

You will start to see performance impacts in the reports once the benchmarks are run from your default branch.

Detected benchmarks

• SegmentList manifest (300 segments/representation): 212.2 ms
• SegmentList manifest (60 segments/representation): 39.3 ms
• SegmentTemplate manifest (50 representations): 11 ms
• SegmentTemplate manifest (small): 3.8 ms

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