🐛 fix: handle response body errors more gracefully in OpenAI handler

Changes:
- Replaced error returns with logging for response body copy failures to prevent early termination of the request.
- Ensured that the response body is closed properly after writing to the client.
- Added comments to clarify the handling of billing and error reporting after the response has been sent.

This update improves error handling and maintains resource management in the OpenAI handler.

relay/channel/openai/relay-openai.go

@@ -623,13 +623,13 @@ func OpenaiHandlerWithUsage(c *gin.Context, resp *http.Response, info *relaycomm
 	c.Writer.WriteHeader(resp.StatusCode)
 	_, err = io.Copy(c.Writer, resp.Body)
 	if err != nil {
-		return service.OpenAIErrorWrapper(err, "copy_response_body_failed", http.StatusInternalServerError), nil
-	}
-	err = resp.Body.Close()
-	if err != nil {
-		return service.OpenAIErrorWrapper(err, "close_response_body_failed", http.StatusInternalServerError), nil
+		common.SysError("error copying response body: " + err.Error())
 	}
+	_ = resp.Body.Close()
 
+	// Once we've written to the client, we should not return errors anymore
+	// because the upstream has already consumed resources and returned content
+	// We should still perform billing even if parsing fails
 	var usageResp dto.SimpleResponse
 	err = json.Unmarshal(responseBody, &usageResp)
 	if err != nil {