Give ShapeStream ability to pause

This could be used manually by people but also a few APIs have come up:

- expose an `enabled` option in `useShape` so people could toggle the stream long polling on and off https://tanstack.com/query/latest/docs/framework/react/guides/disabling-queries
- auto-pause long polling from useShape after the user has been inactive for so long and reactivate it when the user is active again