mailrs-sieve 1.0.0

Clean delivery-action wrapper over Stalwart's `sieve-rs` engine (RFC 5228 Sieve email filtering). Translates the low-level event-loop API into a flat `SieveAction { Keep, FileInto, Discard, Redirect, Reject, Vacation }` enum the caller pattern-matches in its delivery loop. Includes `created_messages` tracking for vacation/notify auto-replies + envelope `From`/`To` injection.