fix: call to sanitize schema for complex union types

[EugeneYushin]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: #5364

Problem:
Using python functions with dicts in its signature breaks Gemini schema.

Solution:
Sanitize schema same way it's done in McpTool

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

> pytest ./tests/unittests
...
=================================================================================== 5531 passed, 2233 warnings in 98.83s (0:01:38) ===================================================================================

Manual End-to-End (E2E) Tests:

• Install changes locally instead of PyPi

google-adk = { path = "<path-to-fork>/adk-python", editable = true }

uv sync --all-packages --group dev
...
Installed 2 packages in 2ms
 ~ adk==0.1.0 (from file:///Users/...)
 - google-adk==1.31.0
 + google-adk==1.31.0 (from file:///...fork/adk-python)

• Follow "Steps to Reproduce" from Issue link

The current UTC timestamp is 2026-04-17T11:46:10.953127+00:00.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

Follow up: #5000

[google-cla]

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[adk-bot]

Response from ADK Triaging Agent

Hello @EugeneYushin, thank you for your contribution!

Before we can proceed with the review, could you please address the following points from the contribution guidelines?

• Contributor License Agreement (CLA): It looks like the CLA check has failed. Please sign the Contributor License Agreement so that we can accept your contribution.
• Manual End-to-End (E2E) Tests: Could you please provide a plan and results for manual end-to-end testing? This is important to verify that the fix works as expected in an integrated environment.

Addressing these items will help us move forward with the review process. Thanks!

[adk-bot]

Response from ADK Triaging Agent

Hello @EugeneYushin, thank you for creating this PR!

Before we can merge this, could you please sign our Contributor License Agreement (CLA)? You can do so here: https://cla.developers.google.com/

Also, could you please provide manual end-to-end (E2E) tests to help us verify the fix?

This information will help reviewers to review your PR more efficiently. Thanks!

[adk-bot]

Response from ADK Triaging Agent

Hello @EugeneYushin, thank you for your contribution!

Before we can merge this PR, we need to address a couple of items from our contribution guidelines:

• CLA: It looks like you haven't signed the Contributor License Agreement (CLA) yet. You can do so at https://cla.developers.google.com/.
• E2E Tests: Could you please provide instructions on how to manually test your changes, including any necessary setup or configuration? Please also provide logs or screenshots to help reviewers better understand the fix.

You can find more information in our contribution guidelines.

Thanks!

[EugeneYushin]

@rohityan could you please take a look? This is somewhat similar to #5000