fix(webrtc)!: make React Native WebRTC an optional peer

[w3lld1]

Description

I moved react-native-webrtc from a runtime dependency to an optional peer, keeping the same version range and a development dependency so the React Native entry point remains available during development. Node.js and browser consumers no longer need to resolve the React Native/Metro subtree.

I documented the explicit React Native installation step in the package documentation and regenerated the README. I added a Node-only regression test for the dependency contract, including the optional peer metadata, development version range, and existing React Native entry-point mapping. The transport runtime is unchanged.

Fixes #3609

BREAKING CHANGE: React Native applications must explicitly install react-native-webrtc@^124.0.6 alongside @libp2p/webrtc; it is no longer installed transitively.

Notes & open questions

I checked this with Node.js 22.23.1 and npm 10.9.8:

• npx eslint src/index.ts test/node.ts — passed.
• npx mocha test/node.ts --timeout 60000 — 1 passing. The same test fails against the upstream package manifest because react-native-webrtc is a regular dependency.
• npm run dep-check in packages/transport-webrtc — passed.
• npx aegir docs --publish false -- --skipErrorChecking — generated the package README; this is documentation generation, not a TypeScript validation result.
• git diff --check — passed.
• I compared isolated npm consumer lockfiles for the upstream manifest and the modified package tarball using npm pack --ignore-scripts --json and default peer resolution with npm install --package-lock-only --ignore-scripts --no-audit --no-fund. The upstream manifest produced 328 lockfile entries including React Native/Metro; the patched tarball produced 104 entries, with no react-native-webrtc, react-native, @react-native/*, Metro, or image-size. This checks dependency resolution, not native execution.

I am leaving the full monorepo build and transport/platform suites to CI. My full build did not complete. The subsequent project-reference TypeScript build and documentation checks were blocked by missing built workspace packages (including @libp2p/gossipsub and @libp2p/noise), so I am not reporting the complete npm run lint or full test suite as passing. I have not tested a React Native application.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

[tabcat]

Thanks!