fix(tasks): survive external CancelledError during connection reset - #10508

Summary

fixes #9074

tasks die after a connection reset, been broken for 3 years mate. basically when the websocket resets it cancels the task externally, that CancelledError was hitting the outer handler and just killing the loop dead. reconnect logic never even got a chance to run innit

shoved an inner CancelledError handler in the try block around coro(). if its an external cancel it backs off and retries, if the user actually asked for a stop it raises like normal

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)