Add GeminiGetHandler, enhance Gemini functionality, and enable token counting

- Added `GeminiGetHandler` for handling GET requests with extended Gemini model support.
- Introduced `geminiCountTokens` function to calculate token usage.
- Refactored `APIRequest` and related methods to support `alt` parameter for enhanced flexibility.
- Updated routes and request processing to integrate new handler and functions.

internal/api/cli-handlers.go

@@ -141,7 +141,7 @@ outLoop:
 			log.Debugf("Request use account: %s, project id: %s", cliClient.GetEmail(), cliClient.GetProjectID())
 		}
 		// Send the message and receive response chunks and errors via channels.
-		respChan, errChan := cliClient.SendRawMessageStream(cliCtx, rawJson)
+		respChan, errChan := cliClient.SendRawMessageStream(cliCtx, rawJson, "")
 		hasFirstResponse := false
 		for {
 			select {
@@ -220,7 +220,7 @@ func (h *APIHandlers) internalGenerateContent(c *gin.Context, rawJson []byte) {
 			log.Debugf("Request use account: %s, project id: %s", cliClient.GetEmail(), cliClient.GetProjectID())
 		}
 
-		resp, err := cliClient.SendRawMessage(cliCtx, rawJson)
+		resp, err := cliClient.SendRawMessage(cliCtx, rawJson, "")
 		if err != nil {
 			if err.StatusCode == 429 && h.cfg.QuotaExceeded.SwitchProject {
 				continue