WIP: Fix intermittent integration test failures

[rwood-moz]

What changed?

Fix some mailstrom intermittent integration test failures.

Why?

The tests are mostly (98%) stable but would be nice to get rid of the intermittent failures.

Limitations and Notes

Changes made by Codex AI; we will see how these changes prove out after a couple weeks in CI. More details:

Changes made so far:

• Fixed IMAP deletion test calls in test_messaging.py and test_messaging.py so single message ids are passed as lists to imap.delete_messages(). This prevents multi-digit ids like "25" from being iterated character-by-character.

• Hardened IMAP.delete_messages() in IMAP.py so it verifies \Deleted by fetching message flags after STORE, rather than depending on the exact shape of the STORE response data.

• Improved JMAP.wait_for_message_to_arrive() in JMAP.py to dynamically resolve the active account’s Inbox id, poll immediately, wait up to 7 minutes, accept one or more matching messages, and log the account/inbox being checked.

• Updated JMAP.query_email() in JMAP.py to make collapse_threads configurable, preserving the existing default while allowing arrival polling to query with collapse_threads=False. This should help self-send CC/BCC tests where collapsed thread results may hide the inbox copy.

Applicable Issues

Fixes #230.

QA Log

• Ran the integration tests on my machine against stage several times, and
• Ran the nightly mailstrom integration tests GHA job against this branch in CI several times.