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](cdf6202156/libs/community/langchain_community/graphs/neo4j_graph.py (L47)),
[Memgraph](cdf6202156/libs/community/langchain_community/graphs/memgraph_graph.py (L50)),
[Kuzu](cdf6202156/libs/community/langchain_community/graphs/kuzu_graph.py (L253)),
and
[Gremlin](cdf6202156/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/tests/integration_tests/graphs/test_age_graph.py

@@ -10,7 +10,11 @@ from langchain_community.graphs.graph_document import GraphDocument, Node, Relat
 
 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"),