Calling `uv_timer_start(h, cb, 0, 0)` from a timer callback resulted in
the timer running immediately because it was inserted at the front of
the timer heap.
If the callback did that every time, libuv would effectively busy-loop
in `uv__run_timers()` and never make forward progress.
Work around that by collecting all expired timers into a queue and only
running their callback afterwards.
Fixes: https://github.com/libuv/libuv/issues/4245
Co-authored-by: Ben Noordhuis <info@bnoordhuis.nl>
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