Make all Cassandra and Qdrant I/O async-safe with proper concurrency controls (#916)

Cassandra triples services were using syncronous EntityCentricKnowledgeGraph
methods from async contexts, and connection state was managed with
threading.local which is wrong for asyncio coroutines sharing a single
thread. Qdrant services had no async wrapping at all, blocking the event
loop on every network call. Rows services had unprotected shared state
mutations across concurrent coroutines.

- Add async methods to EntityCentricKnowledgeGraph (async_insert,
  async_get_s/p/o/sp/po/os/spo/all, async_collection_exists,
  async_create_collection, async_delete_collection) using the existing
  cassandra_async.async_execute bridge
- Rewrite triples write + query services: replace threading.local with
  asyncio.Lock + dict cache for per-workspace connections, use async
  ECKG methods for all data operations, keep asyncio.to_thread only for
  one-time blocking ECKG construction
- Wrap all Qdrant calls in asyncio.to_thread across all 6 services
  (doc/graph/row embeddings write + query), add asyncio.Lock + set cache
  for collection existence checks
- Add asyncio.Lock to rows write + query services to protect shared
  state (schemas, sessions, config caches) from concurrent mutation
- Update all affected tests to match new async patterns

tests/integration/test_rows_cassandra_integration.py

@@ -101,6 +101,8 @@ class TestRowsCassandraIntegration:
         processor.session = None
 
         # Bind actual methods from the new unified table implementation
+        import asyncio
+        processor._setup_lock = asyncio.Lock()
         processor.connect_cassandra = Processor.connect_cassandra.__get__(processor, Processor)
         processor.ensure_keyspace = Processor.ensure_keyspace.__get__(processor, Processor)
         processor.ensure_tables = Processor.ensure_tables.__get__(processor, Processor)
@@ -108,6 +110,7 @@ class TestRowsCassandraIntegration:
         processor.get_index_names = Processor.get_index_names.__get__(processor, Processor)
         processor.build_index_value = Processor.build_index_value.__get__(processor, Processor)
         processor.register_partitions = Processor.register_partitions.__get__(processor, Processor)
+        processor._apply_schema_config = Processor._apply_schema_config.__get__(processor, Processor)
         processor.on_schema_config = Processor.on_schema_config.__get__(processor, Processor)
         processor.on_object = Processor.on_object.__get__(processor, Processor)
         processor.collection_exists = MagicMock(return_value=True)