Add bounded UIDONLY session APIs

[gabeosx]

Summary

Add an opt-in, bounded async-imap API for servers that support UIDONLY,
PARTIAL, and MESSAGELIMIT:

• require exact ENABLE UIDONLY confirmation before entering UIDONLY mode;
• return UIDFETCH results whose leading identifier is always a UID;
• expose ascending and descending PARTIAL ranges for bounded metadata and body
  fetches;
• deliver typed UIDONLY VANISHED events;
• expose MESSAGELIMIT completion instead of silently truncating results;
• enforce caller-configured response and literal ceilings before allocation;
  and
• drain semantic errors through the tagged completion, or poison the session
  when it is unsafe to reuse.

Ordinary FETCH and UID FETCH behavior remains unchanged unless UIDONLY has been
explicitly enabled.

Why

This is the client-library step for rustmailer/bichon#333. Bichon needs a
bounded, typed UIDONLY boundary so it can inventory a fixed UID snapshot,
resume safely, and avoid treating UIDs as mutable message sequence numbers.

Dependencies

• The current-history fork update is Sync fork with current async-imap main #1.
• The required parser support is Add UIDONLY and MESSAGELIMIT response parsing tokio-imap#2.

Until the parser PR is accepted, Cargo.toml pins its exact feature commit,
05439a90033d67297892c3fe206b8c4285df3821, from gabeosx/tokio-imap.
Before this PR merges, that temporary source should be replaced with the
accepted Rustmailer commit or release.

Because this branch is based on #1, GitHub will temporarily show the fork-sync
commits here as well and may report a conflict against the current stale
main. Merge #1 first; this branch is mergeable on that synchronized history.
The UIDONLY API is the single feature commit
905a005234f89d046c2f439cee27daf947917b41.

Verification

• cargo fmt --all -- --check
• async-std: 88 passed
• async-std with compression: 89 passed
• Tokio: 89 passed
• Tokio with compression: 90 passed
• cargo clippy --all -- -D warnings

The focused coverage includes UIDONLY enable confirmation, UIDFETCH/PARTIAL
formatting, VANISHED routing, MESSAGELIMIT completion, malformed responses,
literal/response ceilings, session draining/poisoning, compression handoff,
and ordinary FETCH compatibility.

The Bichon integration using this API is rustmailer/bichon#334.