community: Apache AGE wrapper. Ensure Node Uniqueness by ID. (#28759)

**Description:**

The Apache AGE graph integration incorrectly handled node merging,
allowing duplicate nodes with different IDs but the same type and other
properties. Unlike
[Neo4j](https://github.com/langchain-ai/langchain/blob/cdf62021569dd7f02b35679b46ee6abe92f02cb7/libs/community/langchain_community/graphs/neo4j_graph.py#L47),
[Memgraph](https://github.com/langchain-ai/langchain/blob/cdf62021569dd7f02b35679b46ee6abe92f02cb7/libs/community/langchain_community/graphs/memgraph_graph.py#L50),
[Kuzu](https://github.com/langchain-ai/langchain/blob/cdf62021569dd7f02b35679b46ee6abe92f02cb7/libs/community/langchain_community/graphs/kuzu_graph.py#L253),
and
[Gremlin](https://github.com/langchain-ai/langchain/blob/cdf62021569dd7f02b35679b46ee6abe92f02cb7/libs/community/langchain_community/graphs/gremlin_graph.py#L165),
it did not use the node ID as the primary identifier for merging.

This inconsistency caused data integrity issues and unexpected behavior
when users expected updates to specific nodes by ID.

**Solution:**
This PR modifies the `node_insert_query` to `MERGE` nodes based on label
and ID *only* and updates properties with `SET`, aligning the behavior
with other graph database integrations. The `_format_properties` method
was also modified to handle id overrides.

**Impact:**

This fix ensures data integrity by preventing duplicate nodes, and
provides a consistent behavior across graph database integrations.

libs/community/langchain_community/graphs/age_graph.py

@@ -697,8 +697,9 @@ def add_graph_documents(
         # query for inserting nodes
         node_insert_query = (
             """
-            MERGE (n:`{label}` {properties})
-        """
+            MERGE (n:`{label}` {{`id`: "{id}"}})
+            SET n = {properties}
+            """
             if not include_source
             else """
             MERGE (n:`{label}` {properties})
@@ -735,6 +736,7 @@ def add_graph_documents(
                     query = node_insert_query.format(
                         label=AGEGraph.clean_graph_labels(node.type),
                         properties=self._format_properties(node.properties),
+                        id=node.id,
                     )
 
                 self.query(query)

libs/community/tests/integration_tests/graphs/test_age_graph.py

@@ -10,7 +10,11 @@
 
 test_data = [
     GraphDocument(
-        nodes=[Node(id="foo", type="foo"), Node(id="bar", type="bar")],
+        nodes=[
+            Node(id="foo", type="foo"),
+            Node(id="bar", type="bar"),
+            Node(id="foo", type="foo", properties={"property_a": "a"}),
+        ],
         relationships=[
             Relationship(
                 source=Node(id="foo", type="foo"),