Performance improvements

[Gummilion]

Performance improvements:

1. Skip calling postMessage for StateManager parameters used for metrics overlay when metrics overlay is disabled
2. Simplified animation for Live indicator dot; animate only when controls panel is shown

Specified override for uuid version for sockjs to to fix vulnerability warning in webpack-package example as suggested here .

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[shovtyuk]

@Gummilion
Please add unit coverage for the new reducePost behavior in StateManager.

The performance gain depends on suppressing state:update messages in non-SAB mode, but this is not covered by tests yet. It would be good to verify that:

• with shared: false, port, and reducePost: true, quiet metric-only indexes do not call port.postMessage;
• important state updates still call port.postMessage, for example STATE, CURRENT_TS, VIDEO_LATEST_TS, AUDIO_LATEST_TS, PLAYBACK_START_TS, SILENCE_USEC;
• with reducePost: false, the metric indexes are still posted as before;
• with metricsOverlay: true / reducePost: false, debug overlay behavior is not silently broken.

This would lock down the actual optimization path and protect against accidentally suppressing state needed for playback synchronization.

[shovtyuk]

@Gummilion
src/ui/ui.js: { alpha: false } should not be used for the visible canvas context. The splash screen is applied as a CSS background-image on this._canvas, and an opaque canvas backing store covers it with black. clearRect() also clears to opaque black in this mode, so the splash will not be visible on initial load / stop. Keeping { alpha: false } for the offscreen back buffer is fine, but the visible _cctx should remain transparent.

tests/state-manager.test.js: some MessageChannel assertions are currently weak. postMessageSpy tracks port1.postMessage, but several assertions after counterManager.* writes should check postMessageSpy2 or clear/check the correct spy per step. Listener mocks should also be cleared between waits/tests so assertions cannot pass from stale messages.