standard-tests: refactoring and fixes (#31703)

- `libs/core/langchain_core/messages/base.py`: add model name to
examples [per
docs](https://python.langchain.com/api_reference/standard_tests/integration_tests/langchain_tests.integration_tests.chat_models.ChatModelIntegrationTests.html#langchain_tests.integration_tests.chat_models.ChatModelIntegrationTests.test_usage_metadata)
("0.3.17: Additionally check for the presence of model_name in the
response metadata, which is needed for usage tracking in callback
handlers")
- `libs/core/langchain_core/utils/function_calling.py`: correct typo
-
`libs/standard-tests/langchain_tests/integration_tests/chat_models.py`:
- `magic_function(input)` -> `magic_function(_input)` to prevent warning
about redefining built in `input`
    - relocate a few tests for better grouping and narrative flow
    - suppress some type hint warnings following suit from similar tests
    - fix a few more typos
- validate not only that `model_name` is defined, but that it is not
empty (test_usage_metadata)

libs/core/langchain_core/messages/base.py

@@ -34,7 +34,8 @@ class BaseMessage(Serializable):
     """
 
     response_metadata: dict = Field(default_factory=dict)
-    """Response metadata. For example: response headers, logprobs, token counts."""
+    """Response metadata. For example: response headers, logprobs, token counts, model
+    name."""
 
     type: str
     """The type of the message. Must be a string that is unique to the message type.

libs/core/langchain_core/utils/function_calling.py

@@ -668,7 +668,7 @@ def tool_example_to_messages(
                     ..., description="The color of the person's hair if known"
                 )
                 height_in_meters: Optional[str] = Field(
-                    ..., description="Height in METERs"
+                    ..., description="Height in METERS"
                 )
 
             examples = [