Fix: adds and invokes Neo4jAdapter initialize for schema setup (#933)

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## Description
adds and invokes Neo4jAdapter initialize for schema setup

## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.

cognee/infrastructure/databases/graph/get_graph_engine.py

@@ -16,6 +16,11 @@ async def get_graph_engine() -> GraphDBInterface:
 
     # Async functions can't be cached. After creating and caching the graph engine
     # handle all necessary async operations for different graph types bellow.
+
+    # Run any adapter‐specific async initialization
+    if hasattr(graph_client, "initialize"):
+        await graph_client.initialize()
+
     # Handle loading of graph for NetworkX
     if config["graph_database_provider"].lower() == "networkx" and graph_client.graph is None:
         await graph_client.load_graph_from_file()

cognee/infrastructure/databases/graph/neo4j_driver/adapter.py

@@ -1,5 +1,3 @@
-#
-
 """Neo4j Adapter for Graph Database"""
 
 import json
@@ -52,8 +50,12 @@ class Neo4jAdapter(GraphDBInterface):
             max_connection_lifetime=120,
             notifications_min_severity="OFF",
         )
-        # Create contraint/index
-        self.query(
+
+    async def initialize(self) -> None:
+        """
+        Initializes the database: adds uniqueness constraint on id and performs indexing
+        """
+        await self.query(
             (f"CREATE CONSTRAINT IF NOT EXISTS FOR (n:`{BASE_LABEL}`) REQUIRE n.id IS UNIQUE;")
         )