feat: Handle errors, validate model names, and calculate quota usage

- Improved error handling in various modules for better stability and responsiveness.
- Optimized code in several files for improved efficiency and readability.
- Enhanced user experience by providing more detailed error responses in the controller.
- Strengthened security by ignoring sensitive files in `.gitignore`.

controller/billing.go

@@ -22,7 +22,9 @@ func GetSubscription(c *gin.Context) {
 	} else {
 		userId := c.GetInt("id")
 		remainQuota, err = model.GetUserQuota(userId)
-		usedQuota, err = model.GetUserUsedQuota(userId)
+		if err != nil {
+			usedQuota, err = model.GetUserUsedQuota(userId)
+		}
 	}
 	if expiredTime <= 0 {
 		expiredTime = 0