==(_:_:)

Two identifiers are equal when they have the same shape and the same values: both-local compares local IDs (ignoring stable), both-stable-only compares stable IDs. Mixed shapes (one has local, the other doesn’t) are never equal — this keeps the Hashable contract intact since each shape hashes a different component.

static func == (lhs: SyncableEntityIdentifier<LocalID, StableID>, rhs: SyncableEntityIdentifier<LocalID, StableID>) -> Bool