🪲 BUG-#66: Group multi-clause operands of OR/NOT in IMAP query

[FernandoCelmer]

Summary

• Added _group() helper that wraps multi-clause IMAP search expressions in an outer parenthesis (single search-key group)
• _Expr.__or__ and _Expr.__invert__ now group both operands so the resulting OR / NOT arity matches the Python-level expression
• Single already-grouped clauses stay unwrapped to keep simple expressions readable
• Same fix also resolves Query.exclude / Query.or_ / Query.__or__ / Query.__invert__ since they route through _Expr

Closes #66
Closes #72

Test plan

• pytest tests/clients/imap/test_query.py — 16 passed

[FernandoCelmer]

🔍 Code Review

Code issues found: 0

_group plus _is_balanced correctly preserves IMAP OR/NOT arity. Worth noting the design choices for future readers:

• Singletons stay unwrapped (OR (SUBJECT "a") (SUBJECT "b")) — readable, still RFC 3501 valid.
• Multi-clause operands get one outer paren (OR ((SUBJECT "x") (UNSEEN)) (FROM "a@b")) — collapsed into a single search-key 'list' as the grammar requires.
• _is_balanced toggles inside double quotes so a literal ) inside a value wouldn't break depth counting (not exploitable today since _ascii strips non-ASCII, but defensive).

Closes #66 and #72 in one move since Query.exclude/or_/__or__/__invert__ all route through _Expr.