gh-106751: Optimize SelectSelector.select() for many iteration case

[corona10]

closes: gh-106751

[corona10]

Similar technique can be adopted.

Benchmark

importtimeitimportosfromselectorsimportSelectSelector, EVENT_WRITE, EVENT_READselect=SelectSelector()
for_inrange(100):
r, w=os.pipe()
os.write(w, b"a")
select.register(r, EVENT_READ)
elapsed=timeit.timeit(
"selector.select()",
number=100000,
globals={"selector": select},
)
print(f"elapsed: {elapsed}")

Result

AS-IS: elapsed -> 2.051669834000222
TO-BE: elapsed -> 1.9723411249997298 (1.04x faster)

[corona10]

cc @eendebakpt

[eendebakpt]

Note: on my system frozenset is slightly slower than set, but the difference is very small

[eendebakpt]

The rw is only used once. You assigned r | w to a variable for readability?