Add resource_version-based optimistic concurrency control to the
persistence layer. Every write now requires an explicit WriteCondition
(MustCreate or MatchResourceVersion), enforced at compile time by
gating unconditional put/put_message behind #[cfg(test)].
- Add WriteCondition enum and put_if for conditional writes
- Add update_message_cas for atomic read-modify-write operations
- Add list_messages/list_messages_with_selector helpers that hydrate
resource_version from authoritative DB rows
- Convert all production write paths to CAS-aware methods
- Gate put/put_message behind #[cfg(test)] to prevent non-CAS writes
- Use structured PersistenceError::UniqueViolation matching instead of
string matching for duplicate detection
- Hydrate resource_version from WriteResult directly on creates,
eliminating unnecessary read-after-write round trips
Signed-off-by: Derek Carr <decarr@redhat.com>
Derek Carr