bpo-42064: Adapt sqlite3 to multi-phase init (PEP 489)

[erlend-aasland]

https://bugs.python.org/issue42064

[erlend-aasland]

$ cat measure.py
import gc
import sys

for _ in range(5):
    gc.collect()
    before = sys.gettotalrefcount()

    import sqlite3
    del sys.modules['sqlite3']
    del sqlite3

    gc.collect()
    after = sys.gettotalrefcount()

    print(f"{before=}, {after=}")

$ ./python.exe measure.py
before=51469, after=66883
before=66892, after=66892
before=66892, after=66892
before=66892, after=66892
before=66892, after=66892 

Thank you so much for helping reviewing and improving this, @corona10, @vstinner, @encukou!

For a list of PR's:
$ git log --grep "bpo-\(42064\|41861\|40956\|42862\)" --oneline

[erlend-aasland]

See GH-29230 regarding the docs CI failure.

[encukou]

See GH-29230 regarding the docs CI failure.

PRs can't be merged without passing tests. Could you merge the main branch in?

[vstinner]

Nice! Well done @erlend-aasland!