* feat: support gemini-2.0-flash
- Enhance model support by adding new entries and refining checks for system instruction compatibility.
- Update logging display behavior and adjust default quotas for better user experience.
- Revamp pricing structures in the billing system to reflect current model values and deprecate outdated entries.
- Streamline code by replacing hardcoded values with configurations for maintainability.
* feat: add new Gemini 2.0 flash models to adapter and billing ratio
* fix: update GetRequestURL to support gemini-1.5 model in versioning
* feat: add MILLI_USD constant and update pricing for deepseek services
* feat: add support for new Gemini model version 'gemini-2.0-flash-thinking-exp-01-21'
