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/billing/ratio/group.go

@@ -0,0 +1,34 @@
+package ratio
+
+import (
+	"encoding/json"
+	"github.com/songquanpeng/one-api/common/logger"
+)
+
+var GroupRatio = map[string]float64{
+	"default": 1,
+	"vip":     1,
+	"svip":    1,
+}
+
+func GroupRatio2JSONString() string {
+	jsonBytes, err := json.Marshal(GroupRatio)
+	if err != nil {
+		logger.SysError("error marshalling model ratio: " + err.Error())
+	}
+	return string(jsonBytes)
+}
+
+func UpdateGroupRatioByJSONString(jsonStr string) error {
+	GroupRatio = make(map[string]float64)
+	return json.Unmarshal([]byte(jsonStr), &GroupRatio)
+}
+
+func GetGroupRatio(name string) float64 {
+	ratio, ok := GroupRatio[name]
+	if !ok {
+		logger.SysError("group ratio not found: " + name)
+		return 1
+	}
+	return ratio
+}