test: add missing prompt validation for sync and async resource methods

[dhruvgupta2109]

This pull request adds new tests to ensure that required arguments are properly enforced in the OpenAI Python client, both for synchronous and asynchronous resource methods. The tests verify that appropriate exceptions are raised when mandatory parameters are missing.

Testing improvements:

• Added tests for synchronous methods in the OpenAI client to check that a TypeError is raised when required arguments (such as prompt, image, or model) are missing in completions.create, images.edit, and audio.transcriptions.create methods.
• Added asynchronous tests for the AsyncOpenAI client to verify that missing required arguments in chat.completions.create and images.generate correctly raise a TypeError.

Dependency updates:

• Imported OpenAI and AsyncOpenAI classes in tests/test_required_args.py to support the new tests.