If the websocket reconnects while processing an event, updates are not sent

[masenf]

Describe the bug
An event is tied to a particular websocket sid when it starts processing. If the client token moves to another sid while the event is processing, the resulting update/delta gets dropped. Instead we should send it on the new websocket.

WiP branch: masenf/retry-event-send

To Reproduce

1. app starts background task
2. browser refresh
3. no delta received on new websocket

Specifics (please complete the following information):

• Python Version: 3.13
• Reflex Version: 0.7.9

Additional context
Partial fix posted in the WiP branch, needs a bit more to make it robust

[linear]

ENG-5697 If the websocket reconnects while processing an event, updates are not sent

[masenf]

Fixed in #5805