[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 a50b089)

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

Author: 3 people