tests/uselect_poll_basic: Add basic test for uselect.poll invariants.
tests/uselect_poll_basic: Add basic test for uselect.poll invariants.

This test doesn't check the actual I/O behavior, just "static" invariants
like behavior on duplicate calls or calls when I/O object is not registered
with poller.

MrSurly/micropython,pozetroninc/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,selste/micropython,pfalcon/micropython,henriknelson/micropython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,pramasoul/micropython,pozetroninc/micropython,bvernoux/micropython,henriknelson/micropython,bvernoux/micropython,henriknelson/micropython,trezor/micropython,pramasoul/micropython,tobbad/micropython,adafruit/circuitpython,MrSurly/micropython,pozetroninc/micropython,kerneltask/micropython,bvernoux/micropython,selste/micropython,MrSurly/micropython,selste/micropython,henriknelson/micropython,pozetroninc/micropython,trezor/micropython,pozetroninc/micropython,pramasoul/micropython,pramasoul/micropython,MrSurly/micropython,kerneltask/micropython,trezor/micropython,tobbad/micropython,pfalcon/micropython,trezor/micropython,pfalcon/micropython,tobbad/micropython,MrSurly/micropython,pramasoul/micropython,selste/micropython,kerneltask/micropython,adafruit/circuitpython,tobbad/micropython,pfalcon/micropython,bvernoux/micropython,selste/micropython,tobbad/micropython,pfalcon/micropython,trezor/micropython,kerneltask/micropython,kerneltask/micropython