refactor: standardize dataTag processing across response translators

- Unified `dataTag` initialization by removing spaces after `data:`.
- Replaced manual slicing with `bytes.TrimSpace` for consistent and robust handling of JSON payloads.

internal/client/gemini_client.go

@@ -298,7 +298,7 @@ func (c *GeminiClient) SendRawMessageStream(ctx context.Context, modelName strin
 	handlerType := handler.HandlerType()
 	rawJSON = translator.Request(handlerType, c.Type(), modelName, rawJSON, true)
 
-	dataTag := []byte("data: ")
+	dataTag := []byte("data:")
 	errChan := make(chan *interfaces.ErrorMessage)
 	dataChan := make(chan []byte)
 	// log.Debugf(string(rawJSON))
@@ -342,7 +342,7 @@ func (c *GeminiClient) SendRawMessageStream(ctx context.Context, modelName strin
 				for scanner.Scan() {
 					line := scanner.Bytes()
 					if bytes.HasPrefix(line, dataTag) {
-						lines := translator.Response(handlerType, c.Type(), newCtx, modelName, originalRequestRawJSON, rawJSON, line[6:], &param)
+						lines := translator.Response(handlerType, c.Type(), newCtx, modelName, originalRequestRawJSON, rawJSON, bytes.TrimSpace(line[5:]), &param)
 						for i := 0; i < len(lines); i++ {
 							dataChan <- []byte(lines[i])
 						}
@@ -353,7 +353,7 @@ func (c *GeminiClient) SendRawMessageStream(ctx context.Context, modelName strin
 				for scanner.Scan() {
 					line := scanner.Bytes()
 					if bytes.HasPrefix(line, dataTag) {
-						dataChan <- line[6:]
+						dataChan <- bytes.TrimSpace(line[5:])
 					}
 					c.AddAPIResponseData(ctx, line)
 				}