fix: invalidate stale video renderer attachments and respect ownership

[bdlukaa]

Problem

VideoTrackRenderer can finish renderer initialization or listener replacement after its track has changed or its widget has been disposed. A stale async attachment can then install a listener for the wrong track or update a rendererthat no longer belongs to that widget State.

Reproduction

Delay renderer initialization or disposal of the current track listener. While it is pending, replace the track (including A → B → C) or unmount the widget.
The previous attachment has no validity check after its await.

Fix

• Invalidate in-flight attachments when the track, renderer, effective render mode, or widget lifecycle changes.
• Keep initialization work out of repeated builds and attach only for the current generation.
• Guard stream and resize callbacks against stale generations.
• Detach cached renderers without disposing caller-owned instances; dispose widget-owned renderers according to autoDisposeRenderer.

[devin-ai-integration]

Devin Review found 1 new potential issue.

1 flag not posted on this PR by your GitHub settings — view it in Devin Review. (Configure)

[bdlukaa]

This is not a breaking change as the tests say. The API is the same.