fix: Exclude None/null values in request data

[SootyOwl]

Please describe the purpose of this pull request.

Prevents sending null values to OpenAI-compatible endpoints. Optional parameters should be excluded entirely - don't rely on endpoints to handle null values identically.

Fixes a 400 error I was having when using https://synthetic.new as my OpenAI-proxy, specifically when attempting to run summarization.

How to test
Run summarization and verify that the request made no longer contains {..., "tools": null, "tool_choice": null}

Have you tested this PR?

Only by manually sending requests to my chosen endpoint to verify what the issue was.

Summarization API response with nulls:

Details

``` Error code: 400, Response JSON: {'error': '[object Object] failed the following checks:\n' '[object Object] failed the following checks:\n' 'null is not an array\n' 'null failed the following checks:\n' 'null failed the following checks:\n' 'null is not equal to auto\n' 'null failed the following checks:\n' 'null is not equal to none\n' 'null is not equal to required\n' 'null is null\n' "missing key 'stream'\n" '[object Object] failed the following checks:\n' 'null is not an array\n' 'null failed the following checks:\n' 'null failed the following checks:\n' 'null is not equal to auto\n' 'null failed the following checks:\n' 'null is not equal to none\n' 'null is not equal to required\n' 'null is null'} ```

Summarization API response without nulls:

Details

``` Code: 200, Response JSON: {'choices': [...], 'created': 1762445699, 'id': '6c8e5475-33bb-4679-8158-d350262d8fd6', 'model': 'accounts/fireworks/models/gpt-oss-120b', 'object': 'chat.completion', 'usage': {...}} ```