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/client/init.go

@@ -0,0 +1,36 @@
+package client
+
+import (
+	"net/http"
+	"os"
+	"time"
+
+	gutils "github.com/Laisky/go-utils/v4"
+	"github.com/songquanpeng/one-api/common/config"
+)
+
+var HTTPClient *http.Client
+var ImpatientHTTPClient *http.Client
+
+func init() {
+	var opts []gutils.HTTPClientOptFunc
+
+	timeout := time.Duration(max(config.IdleTimeout, 30)) * time.Second
+	opts = append(opts, gutils.WithHTTPClientTimeout(timeout))
+	if os.Getenv("RELAY_PROXY") != "" {
+		opts = append(opts, gutils.WithHTTPClientProxy(os.Getenv("RELAY_PROXY")))
+	}
+
+	var err error
+	HTTPClient, err = gutils.NewHTTPClient(opts...)
+	if err != nil {
+		panic(err)
+	}
+
+	ImpatientHTTPClient, err = gutils.NewHTTPClient(
+		gutils.WithHTTPClientTimeout(5 * time.Second),
+	)
+	if err != nil {
+		panic(err)
+	}
+}