- 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
- Updated error handling across multiple files with `Laisky/errors/v2` package
- Replaced hardcoded error messages with `Laisky/errors` in relay/channel/tencent/adaptor.go
- Added a function to check if a request should be retried in relay/controller/relay.go
- Removed unused imports and variables, and updated comments in various files
- Changed Redis cache handling in model/cache.go
- Refactored error handling in relay/channel/tencent/main.go and relay/channel/baidu/main.go
- Updated import paths and error handling in model/user.go, model/redemption.go, and controller/github.go
- Added import for tiktoken-go package in relay/channel/openai/token.go
- Added GetSign and ParseConfig functions in relay/channel/tencent/main.go
- Replaced specific error imports with a more general one in relay/channel/ali/adaptor.go
- Updated import comments and function calls in relay/channel/ali/adaptor.go
- Added checks and custom error messages in model/token.go
- Removed unused functions and variables in relay/channel/baidu/adaptor.go
- Imported "github.com/Laisky/errors/v2" package in controller/channel-billing.go
- Removed unused import packages in [relay/channel/tencent/adaptor.go](http://relay/channel/tencent/adaptor.go) and relay/channel/palm/adaptor.go
- Updated go.mod and go.sum files with new dependencies and versions
