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.go

@@ -0,0 +1,41 @@
+package relay
+
+import (
+	"github.com/songquanpeng/one-api/relay/adaptor"
+	"github.com/songquanpeng/one-api/relay/adaptor/aiproxy"
+	"github.com/songquanpeng/one-api/relay/adaptor/anthropic"
+	"github.com/songquanpeng/one-api/relay/adaptor/gemini"
+	"github.com/songquanpeng/one-api/relay/adaptor/ollama"
+	"github.com/songquanpeng/one-api/relay/adaptor/openai"
+	"github.com/songquanpeng/one-api/relay/adaptor/palm"
+	"github.com/songquanpeng/one-api/relay/apitype"
+)
+
+func GetAdaptor(apiType int) adaptor.Adaptor {
+	switch apiType {
+	case apitype.AIProxyLibrary:
+		return &aiproxy.Adaptor{}
+	// case apitype.Ali:
+	// 	return &ali.Adaptor{}
+	case apitype.Anthropic:
+		return &anthropic.Adaptor{}
+	// case apitype.Baidu:
+	// 	return &baidu.Adaptor{}
+	case apitype.Gemini:
+		return &gemini.Adaptor{}
+	case apitype.OpenAI:
+		return &openai.Adaptor{}
+	case apitype.PaLM:
+		return &palm.Adaptor{}
+	// case apitype.Tencent:
+	// 	return &tencent.Adaptor{}
+	// case apitype.Xunfei:
+	// 	return &xunfei.Adaptor{}
+	// case apitype.Zhipu:
+	// 	return &zhipu.Adaptor{}
+	case apitype.Ollama:
+		return &ollama.Adaptor{}
+	}
+
+	return nil
+}