[Flight] Close Debug Channel when All Lazy References Have Been GC:ed #33718
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…33719) Stacked on #33718. Alternative to #33716. The issue with flushing the Server Components track in its current form is that we need to decide how long to wait before flushing whatever we have. That's because the root's end time will be determined by the end time of that last child. However, if a child isn't actually used then we don't necessarily need to include it in the Server Components track since it wasn't blocking the initial render. This waits for 100ms after the last pending chunk is resolved and if nothing is invoking any more lazy initializers after that then we log the Server Components track with the information we have at that point. We also don't eagerly initialize any chunks that wasn't already initialized so if nothing was rendered, then nothing will be logged. This is somewhat an artifact of the current visualization. If we did another transposed form we wouldn't necessarily need to wait until the end and can log things as they're discovered.
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When we have a debug channel open that can ask for more objects. That doesn't close until all lazy objects have been explicitly asked for. If you GC an object before the lazy references inside of it before asking for or releasing the objects, then it'll never close.
This ensures that if there are no more PendingChunk and no more ResolvedModelChunk then we can close the connection.
There's two sources of retaining the Response object. On one side we have a handle to it from the stream coming from the server. On the other side we have a handle to it from ResolvedModelChunk to ask for more data when we lazily parse a model.
This PR makes a weak handle from the stream to the Response. However, it keeps a strong reference alive whenever we're waiting on a pending chunk because then the stream might be the root if the only listeners are the callbacks passed to the promise and no references to the promise itself.
The pending chunks count can end up being zero even if we might get more data because the references might be inside lazy chunks. In this case the lazy chunks keeps the Response alive. When the lazy chunk gets parsed it can find more chunks that then end up pending to keep the response strongly alive until they resolve.