[event-loop] Don't crash by running removed timeouts

[event-loop] Don't crash by running removed timeouts

We used to run and remove timeouts in a loop.  This
breaks the case where the dispatched timeout handler
removes the timeout itself.

We fix it by making timeout handling a two pass thing.
First we find which handlers need to be dispatched,
and move them to their own list.  Then we run through
the new list and dispatch the handlers.