fix(watch): properly shut down persistent tasks (#8854)
### Description
Previously when we decided we needed to restart persistent tasks we
would just call `abort()` on the task handle. This was incorrect as our
child processes don't get shut down on drop. This resulted in ports not
getting freed up from these zombie tasks.
The fix is to create a new `RunStopper` struct which just has a handle
on the child process manager so we can shut down the individual children
before aborting the entire task. We also move the persistent task shut
down to happen before we update the TUI task list so we don't finish
tasks that never started.
### Testing Instructions
Before:
https://github.com/user-attachments/assets/54630a33-44f9-4d73-b70d-5e0800b239fa
After:
https://github.com/user-attachments/assets/f5379795-46f2-424b-b136-1da345882106
