Add CentML Provider

[anurlybayev]

Add CentML Provider Support

Description

Added support for CentML, to expand aisuite's provider options.

Changes Made

• Added CentML provider implementation in providers/centml_provider.py
• Added necessary environment variables for CentML API authentication

Testing

• Tested provider initialization
• Tested chat completion functionality
• All existing tests pass

Environment Variables Added

CENTML_API_KEY=

Related Documentation

• Added CentML to the list of supported providers in README.md

Checklist

• Code follows project style guidelines
• Updated documentation
• Pre-commit hooks pass

[anurlybayev]

@ksolo can you please review?

[anurlybayev]

@ksolo @rohitprasad15 I rebased my branch from main. Can you please review?

[rohitprasad15]

Thanks for the PR. Please re-test after the addition of pydantic checks in the codebase.
If possible, please add tool calling support as well.
If the model uses OpenAI message format, then you can use Mistral or Together as an example on how to use an existing base class to do message conversion.
Please tag me after changes are done.