[Tool] Fix auto tool call

[heheda12345]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

Fix tool call tests in tests/tool_use

Test Plan

Run these tests.

Test Result

test_chat_completions.py::test_chat_completion_without_tools passed locally. Let's run other tests in CI.

(Optional) Documentation Update

[gemini-code-assist]

Code Review

This pull request refactors the validation for tool usage in the Responses API. The change correctly moves the check for tool support from server initialization to request time, and scopes it to the Responses API for non-Harmony models. This is a good improvement as it prevents the tool-use feature flag from incorrectly blocking other APIs like ChatCompletion at startup. The implementation looks correct and robust. I approve these changes.

[github-actions]

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[DarkLight1337]

Thanks for fixing