Previously, every operation in `socket` would release the GIL, allowingother threads to progress. This makes sense when using threads andblocking sockets, but when using non-blocking sockets (as done withasyncio) these operations return quickly. In the presence of backgroundthreads this can lead to the "convoy effect", where the GIL is acquiredand held by the background thread every time the IO thread releases it,and then the IO thread blocks until it regains ownership of the GIL,causing a massive decrease in IO operations per second.One possible fix for this is to have IO-heavy threads release the GILless frequently. In the case of asyncio, the following changes wereneeded:- Don't release the GIL for socket operations on non-blocking sockets.- Don't release the GIL for select (epoll, select, kqueue, ...) callswith a timeout of 0.With these changes, asyncio doesn't see as degraded of an output when abackground thread holds the GIL.