ensure official openai tool-use json format

[aniketmaurya]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

This PR will make sure to use the standard official OpenAI tool-use structure and boost compatibility with other APIs.

• Update LitTool schema structure to include function type and nested function details as per standard OpenAI format.
• Updated the as_tool method in LitTool to return a schema with a "type" field and a nested "function" object containing name, description, and parameters.
• Modified corresponding unit tests to validate the new schema structure for various tools, ensuring compatibility with the updated format.

PR review

Anyone in the community is free to review the PR once the tests have passed.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88%. Comparing base (d74c924) to head (d39d15e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage    88%   88%           
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  Hits        333   333           
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