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/meta/relay_meta.go

@@ -0,0 +1,59 @@
+package meta
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/songquanpeng/one-api/common/config"
+	"github.com/songquanpeng/one-api/relay/adaptor/azure"
+	"github.com/songquanpeng/one-api/relay/channeltype"
+	"github.com/songquanpeng/one-api/relay/relaymode"
+	"strings"
+)
+
+type Meta struct {
+	Mode            int
+	ChannelType     int
+	ChannelId       int
+	TokenId         int
+	TokenName       string
+	UserId          int
+	Group           string
+	ModelMapping    map[string]string
+	BaseURL         string
+	APIVersion      string
+	APIKey          string
+	APIType         int
+	Config          map[string]string
+	IsStream        bool
+	OriginModelName string
+	ActualModelName string
+	RequestURLPath  string
+	PromptTokens    int // only for DoResponse
+	ChannelRatio    float64
+}
+
+func GetByContext(c *gin.Context) *Meta {
+	meta := Meta{
+		Mode:           relaymode.GetByPath(c.Request.URL.Path),
+		ChannelType:    c.GetInt("channel"),
+		ChannelId:      c.GetInt("channel_id"),
+		TokenId:        c.GetInt("token_id"),
+		TokenName:      c.GetString("token_name"),
+		UserId:         c.GetInt("id"),
+		Group:          c.GetString("group"),
+		ModelMapping:   c.GetStringMapString("model_mapping"),
+		BaseURL:        c.GetString("base_url"),
+		APIVersion:     c.GetString(config.KeyAPIVersion),
+		APIKey:         strings.TrimPrefix(c.Request.Header.Get("Authorization"), "Bearer "),
+		Config:         nil,
+		RequestURLPath: c.Request.URL.String(),
+		ChannelRatio:   c.GetFloat64("channel_ratio"),
+	}
+	if meta.ChannelType == channeltype.Azure {
+		meta.APIVersion = azure.GetAPIVersion(c)
+	}
+	if meta.BaseURL == "" {
+		meta.BaseURL = channeltype.ChannelBaseURLs[meta.ChannelType]
+	}
+	meta.APIType = channeltype.ToAPIType(meta.ChannelType)
+	return &meta
+}