[3.15] gh-66335: Add tests for imaplib command methods (GH-152872) (GH-152873)

[3.15] gh-66335: Add tests for imaplib command methods (GH-152872) (GH-152873)

Add coverage tests for the IMAP4 command methods and their UID variants
(SELECT, CREATE, COPY, STORE, FETCH, SEARCH, SORT, THREAD, DELETE,
RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, STATUS, the ACL and quota
commands, ANNOTATION, PROXYAUTH and ENABLE), plus test helpers
(splitargs, parse_sequence_set, make_simple_handler) and per-command
argument capture in the test server.
(cherry picked from commit a50b089b7c46e3068d9177b5f18ac767a31a18cd)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>