gh-66335: Add tests for imaplib command methods

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.

The tests assert the current wire behavior; a follow-up for gh-40038
updates the expected values once argument quoting is restored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka