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/unit/test_query/test_rows_cassandra_query.py

@@ -89,12 +89,15 @@ class TestRowsGraphQLQueryLogic:
     @pytest.mark.asyncio
     async def test_schema_config_parsing(self):
         """Test parsing of schema configuration"""
+        import asyncio
         processor = MagicMock()
         processor.schemas = {}
         processor.schema_builders = {}
         processor.graphql_schemas = {}
         processor.config_key = "schema"
         processor.query_cassandra = MagicMock()
+        processor._setup_lock = asyncio.Lock()
+        processor._apply_schema_config = Processor._apply_schema_config.__get__(processor, Processor)
         processor.on_schema_config = Processor.on_schema_config.__get__(processor, Processor)
 
         # Create test config
@@ -335,7 +338,7 @@ class TestUnifiedTableQueries:
         """Test query execution with matching index"""
         processor = MagicMock()
         processor.session = MagicMock()
-        processor.connect_cassandra = MagicMock()
+        processor.connect_cassandra = AsyncMock()
         processor.sanitize_name = Processor.sanitize_name.__get__(processor, Processor)
         processor.get_index_names = Processor.get_index_names.__get__(processor, Processor)
         processor.find_matching_index = Processor.find_matching_index.__get__(processor, Processor)
@@ -396,7 +399,7 @@ class TestUnifiedTableQueries:
         """Test query execution without matching index (scan mode)"""
         processor = MagicMock()
         processor.session = MagicMock()
-        processor.connect_cassandra = MagicMock()
+        processor.connect_cassandra = AsyncMock()
         processor.sanitize_name = Processor.sanitize_name.__get__(processor, Processor)
         processor.get_index_names = Processor.get_index_names.__get__(processor, Processor)
         processor.find_matching_index = Processor.find_matching_index.__get__(processor, Processor)