Speed up `socket.errorTab` and lazy import `selectors`

[Wulian233]

Feature or enhancement

>python -m timeit -n 1000 -s "import socket" "print(socket.__all__)"
1000 loops, best of 5: 407 usec per loop

>python -m timeit -n 1000 -s "import socket" "print(socket.__all__)"
1000 loops, best of 5: 352 usec per loop

1.15x faster

Linked PRs

• gh-121423: Improve import time of socket by writing socket.errorTab as a constant and lazy import modules #121424

[vstinner]

Implemented by 7bd964d.