* 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- Revamp pricing structures in the billing system to reflect current model values and deprecate outdated entries.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
- 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- Revamp pricing structures in the billing system to reflect current model values and deprecate outdated entries.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 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'
* Update model.go
* Support Gemini tool_calls.
* Fix gemini tool calls (also keep support functions).
* Fixed the problem of arguments not being stringified.
Fix panic: candidate.Content.Parts out of range
- Refactor constant definitions and organization
- Clean up package level variables and functions
- Introduce new `relaymode` and `apitype` packages for constant definitions
- Refactor and simplify code in several packages including `openai`, `relay/channel/baidu`, `relay/util`, `relay/controller`, `relay/channeltype`
- Add helper functions in `relay/channeltype` package to convert channel type constants to corresponding API type constants
- Remove deprecated functions such as `ResponseText2Usage` from `relay/channel/openai/helper.go`
- Modify code in `relay/util/validation.go` and related files to use new `validator.ValidateTextRequest` function
- Rename `util` package to `relaymode` and update related imports in several packages
