Refactor codebase, introduce relaymode package, update constants and improve consistency

- 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

relay/adaptor/zhipu/model.go

@@ -0,0 +1,46 @@
+package zhipu
+
+// import (
+// 	"github.com/songquanpeng/one-api/relay/model"
+// 	"time"
+// )
+
+// type Message struct {
+// 	Role    string `json:"role"`
+// 	Content string `json:"content"`
+// }
+
+// type Request struct {
+// 	Prompt      []Message `json:"prompt"`
+// 	Temperature float64   `json:"temperature,omitempty"`
+// 	TopP        float64   `json:"top_p,omitempty"`
+// 	RequestId   string    `json:"request_id,omitempty"`
+// 	Incremental bool      `json:"incremental,omitempty"`
+// }
+
+// type ResponseData struct {
+// 	TaskId      string    `json:"task_id"`
+// 	RequestId   string    `json:"request_id"`
+// 	TaskStatus  string    `json:"task_status"`
+// 	Choices     []Message `json:"choices"`
+// 	model.Usage `json:"usage"`
+// }
+
+// type Response struct {
+// 	Code    int          `json:"code"`
+// 	Msg     string       `json:"msg"`
+// 	Success bool         `json:"success"`
+// 	Data    ResponseData `json:"data"`
+// }
+
+// type StreamMetaResponse struct {
+// 	RequestId   string `json:"request_id"`
+// 	TaskId      string `json:"task_id"`
+// 	TaskStatus  string `json:"task_status"`
+// 	model.Usage `json:"usage"`
+// }
+
+// type tokenData struct {
+// 	Token      string
+// 	ExpiryTime time.Time
+// }