A full batch of 64 events polled again without returning to the event
loop. When synchronous socket callbacks kept 64 events ready on every
drain, timers and setImmediate callbacks never ran. The poll phase now
drains at most 48 full batches, the count libuv's uv__io_poll uses, and
the budget carries across the reopen that lets microtasks run, so the
remaining events wait for the next loop iteration.
Chris Tate
c2ae71a6fa