fix: Refactor relay/channel, upgrade deps, improve request handling and error messages.

* Updated relay/channel/gemini package to use gin-gonic/gin for routing
* Added timeouts, environment variable for proxy, and error handling for HTTP clients in relay/util/init.go
* Improved error handling, URL path cases, and channel selection logic in middleware/distributor.go
* Added Content-Type header, closed request bodies, and added context to requests in relay/channel/common.go
* Upgraded various dependencies in go.mod
* Modified the GetRequestURL method in relay/channel/gemini/adaptor.go to include a "key" parameter in the URL and set a default version of "v1beta"
* Added io and net/http packages in relay/channel/gemini/adaptor.go and relay/channel/gemini/main.go
* Added a struct for GeminiStreamResp and modified response handling in relay/channel/gemini/main.go
* Imported packages for io and net/http added, gin-gonic/gin package added, and error handling improved in relay/channel/gemini/main.go

common/gin.go

@@ -3,9 +3,10 @@ package common
 import (
 	"bytes"
 	"encoding/json"
-	"github.com/gin-gonic/gin"
 	"io"
 	"strings"
+
+	"github.com/gin-gonic/gin"
 )
 
 const KeyRequestBody = "key_request_body"