[opentelemetry-instrumentation-google-genai] Add tool definitions attribute on interactions API, other minor changes

[DylanRussell]

Description

Added tool definitions attribute on the interactions API spans.

Function calling for interactions API is described at: https://ai.google.dev/gemini-api/docs/function-calling

Note that automatic function calling is not yet supported, so we can't get the execute tool spans like we do with generate_content instrumentation. The user is on the hook for calling their own functions..

I used GenericToolDefinition to capture built in tools and MCP server being provided as tools to the API..

I also updated the code to use the invoke remote agent span when an agent is specified instead of an inference span since a remote agent is being called.

I deleted obsolete TODOs and updated the README.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How has this been tested?

Unit tests

Checklist

See CONTRIBUTING.md
for the style guide, changelog guidance, and more.

• Followed the style guidelines of this project
• Changelog updated if the change requires an entry
• Unit tests added
• Documentation updated

[Copilot]

Pull request overview

This PR updates the Google GenAI SDK instrumentation to better reflect the Interactions API’s tool usage and agent invocation semantics, and aligns user-facing docs/tests accordingly.

Changes:

• Add gen_ai.tool.definitions capture on interactions.create spans by mapping Interactions “tools” inputs into ToolDefinition models.
• Emit invoke_agent spans (via TelemetryHandler.invoke_remote_agent) when an agent is provided, instead of using an inference span shape.
• Remove obsolete TODO documentation and update the package README to describe current limitations/behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

File	Description
instrumentation/opentelemetry-instrumentation-google-genai/TODOS.md	Removes obsolete TODO list now that README describes current limitations.
instrumentation/opentelemetry-instrumentation-google-genai/tests/interactions/base.py	Adds unit coverage for agent spans and tool definition serialization on interactions spans.
instrumentation/opentelemetry-instrumentation-google-genai/src/opentelemetry/instrumentation/google_genai/interactions.py	Implements tool definition extraction for Interactions API and switches to invoke_agent when agent is specified.
instrumentation/opentelemetry-instrumentation-google-genai/README.rst	Updates docs to reflect newly instrumented APIs and limitations around function calling for interactions.

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