Combine crypto-related `receiveSyncChanges` calls into one (#5503)
* test: make sync fixtures report one-time key counts like a real server
* test: wait for sync processing before asserting on sync-driven events
* SlidingSync: dispatch extensions sequentially and add onResponseComplete
* chore: Bump @matrix-org/matrix-sdk-crypto-wasm to ^18.6.0
* refactor: Pass all E2EE sync data to the OlmMachine in a single call