When entered by the root actor avoid excessive polling cycles by,
- blocking on the `Lock.no_remote_has_tty: trio.Event` and breaking
*immediately* when set (though we should really also lock
it from the root right?) to avoid extra loops..
- shielding the `await trio.sleep(poll_delay)` call to avoid any local
cancellation causing the (presumably root-actor task) caller to move
on (possibly to cancel its children) and instead to continue
poll-blocking until the lock is actually released by its user.
- `break` the poll loop immediately if no remote locker is detected.
- use `.pdb()` level for reporting lock state changes.
Also add a #TODO to handle calls by non-root actors as it pertains to