Description

Based on #3941 which is based on #3879

• Add Endpoint::closed, which returns a CancellationToken that is cancelled once the endpoint is closing
• Document watcher behavior with regards to closing the endpoint
• Fix test

Breaking Changes

Notes & open questions

• Instead of returning a CancellationToken we could make this an async fn, however to me it looks quite useful to get a CancellationToken and be able to use tokio::spawn(endpoint_closed.run_until_cancelled_owned(async move { .. })))
• The cancellation token is cancelled when Endpoint::close starts, not when it ends. I wasn't sure what expected behavior is here. I opted for start because this guarantees that the endpoint is fully usable until then.

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.
  • List all breaking changes in the above "Breaking Changes" section.
  • Open an issue or PR on any number0 repos that are affected by this breaking change. Give guidance on how the updates should be handled or do the actual updates themselves. The major ones are:
    • quic-rpc
    • iroh-gossip
    • iroh-blobs
    • dumbpipe
    • sendme