feat: Implement improved side effects cleaning

[benjaminrobinet]

I faced some performance issues after few Renderer creation / closing.
Tried to improve it a bit. Might contain some AI slope.

Summary

• Cancellable stream loop — Demuxer.demuxStream now returns a cancel() function. Calling it stops the background read loop, cancels the underlying reader, and rejects any pending loaded() promises. Previously the loop ran to completion regardless of whether the consumer was still alive.

• Decoder tears down its stream on close — Decoder stores the cancel from demuxStream and calls it in close() (and before starting a new loadStream). The onLoadFrames callback and all frame callbacks guard against closed, so no frames are processed and no VideoDecoder is touched after teardown.

• No more VideoDecoder resurrection — TrackDecoder.set() now returns immediately when closed instead of reconfiguring a closed VideoDecoder. TrackDecoder.load() re-creates the decoder lazily when reloading after a close, keeping the load → close → load cycle working. output() also guards against being called post-close.

• Complete and idempotent Renderer.close() — The VAO is now deleted, all GL handles are nulled after deletion, and WEBGL_lose_context.loseContext() is called to immediately free the WebGL2 context slot (browsers cap active contexts at ~8–16; exceeding this caused the freezing). close() is safe to call multiple times. Public methods (load, loadStream, seek, progress, set, initialize) throw 'Renderer is closed' after teardown.

[vercel]

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[juliendargelos]

Thanks, can you add tests for the new behaviors introduced by these changes ?

[benjaminrobinet]

Done @juliendargelos :)