fix: report zero volume from useTrackVolume

[RaphaelFakhri]

Fixes useTrackVolume so it reports silence.

The native volume processors emit volume: 0 when a track is silent or muted. The event handler checked event.volume for truthiness, so a value of 0 was ignored and the hook kept returning the last non-zero volume. A level meter built on the hook stays stuck at its last level after the speaker stops.

The handler now only skips events where volume is null or undefined.

This change also:

• Adds a jest test that emits a non-zero volume followed by 0 and expects the hook to return 0. The test fails on the previous code.
• Adds react-test-renderer as a dev dependency to render the hook in the test.
• Sets the jest testEnvironment to node. With the react-native preset environment, jest 30 fails to start with this._moduleMocker.clearMocksOnScope is not a function because the preset resolves its own older jest-mock.
• Excludes __tests__ from tsconfig.build.json so yarn typescript and the build ignore test files.
• Adds a changeset.

Test plan:

• yarn jest fails before the source change (1 failed) and passes after (1 passed).
• yarn lint and yarn typescript pass.

[changeset-bot]

🦋 Changeset detected

Latest commit: 69dfd23

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@livekit/react-native	Patch

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[CLAassistant]

All committers have signed the CLA.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.