fix(google-genai): prevent TypeError when handling Pydantic model class

[arloc]

Description

This PR fixes a bug in the opentelemetry-instrumentation-google-genai package where passing an uninstantiated Pydantic model class (instead of an instance) to dict conversion functions would cause a TypeError:

BaseModel.model_dump() missing 1 required positional argument: 'self' 

The issue occurred in three functions that attempt to convert objects to dictionaries:

• _to_dict() in generate_content.py
• _to_otel_value() in tool_call_wrapper.py
• _flatten_dict() in dict_util.py

These functions check hasattr(value, "model_dump") which returns True for both Pydantic classes and instances, but model_dump() is an instance method that cannot be called on the class itself.

Solution:

• Added isinstance(value, type) check to distinguish between classes and instances before calling model_dump()
• When a Pydantic class is detected, the code now calls model_json_schema() (a classmethod) to get the schema representation
• Added comprehensive test coverage for both class and instance scenarios

Fixes #3596

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Added unit tests to verify the fix:

1. test_flatten_with_pydantic_class_not_instance in tests/utils/test_dict_util.py

   • Verifies that passing a Pydantic class (not instance) doesn't raise the model_dump() error
   • Confirms the class is properly serialized using model_json_schema()

2. test_handles_pydantic_class_not_instance in tests/utils/test_tool_call_wrapper.py

   • Tests the same scenario for the tool call wrapper functionality
   • Ensures proper handling of Pydantic model classes in tool call contexts

Does This PR Require a Core Repo Change?

• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated (not needed - internal implementation fix)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: arloc / name: Davi Campos (6045ec2)

[aabmass]

@DylanRussell this covers some of the same things as #3905, but also includes the JSON schema. WDYT?

[DylanRussell]

I just put str(Class) when I came across this. This also works, but it's a lot more information.. Do we want the whole json schema each time ?

[aabmass]

We have a semconv PR for tool schemas open-telemetry/semantic-conventions#2942. I think it's generally useful but maybe best to hold off until we have conventions. @arloc was capturing the schema in particular important to you or mostly just avoiding this exception?

[aabmass]

We merged #2942, but I'll leave this open until we decide on including the json schema inline.