Add $ai_lib_metadata assertions to provider tests

Add missing $ai_lib_metadata assertions to Anthropic, Gemini, and LangChain tests to match the validation already present in OpenAI tests. Each test now verifies the metadata field contains the correct schema version and framework name.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: andrewm4894

posthog/test/ai/anthropic/test_anthropic.py

@@ -293,6 +293,10 @@ def test_basic_completion(mock_client, mock_anthropic_response):
 
         assert call_args["distinct_id"] == "test-id"
         assert call_args["event"] == "$ai_generation"
+        assert props["$ai_lib_metadata"] == {
+            "schema": "v1",
+            "frameworks": [{"name": "anthropic"}],
+        }
         assert props["$ai_provider"] == "anthropic"
         assert props["$ai_model"] == "claude-3-opus-20240229"
         assert props["$ai_input"] == [{"role": "user", "content": "Hello"}]

posthog/test/ai/gemini/test_gemini.py

@@ -167,6 +167,10 @@ def test_new_client_basic_generation(
 
     assert call_args["distinct_id"] == "test-id"
     assert call_args["event"] == "$ai_generation"
+    assert props["$ai_lib_metadata"] == {
+        "schema": "v1",
+        "frameworks": [{"name": "gemini"}],
+    }
     assert props["$ai_provider"] == "gemini"
     assert props["$ai_model"] == "gemini-2.0-flash"
     assert props["$ai_input_tokens"] == 20

posthog/test/ai/langchain/test_callbacks.py

@@ -204,6 +204,10 @@ def test_basic_chat_chain(mock_client, stream):
     # Generation is second
     assert generation_args["event"] == "$ai_generation"
     assert "distinct_id" in generation_args
+    assert generation_props["$ai_lib_metadata"] == {
+        "schema": "v1",
+        "frameworks": [{"name": "langchain"}],
+    }
     assert "$ai_model" in generation_props
     assert "$ai_provider" in generation_props
     assert generation_props["$ai_input"] == [