fix: enhance MongoDB client connection error handling

- Added a ping check after establishing a MongoDB client connection to ensure the connection is valid.
- Implemented error logging for ping failures to improve debugging and provide clearer feedback on connection issues.
- Ensured alignment with existing error handling practices in the codebase for consistency and maintainability.

core/mongo/client.go

@@ -136,6 +136,11 @@ func newMongoClient(_opts *ClientOptions) (c *mongo.Client, err error) {
 		if err != nil {
 			return err
 		}
+		err = c.Ping(ctx, nil)
+		if err != nil {
+			logger.Errorf("ping mongo error: %v", err)
+			return err
+		}
 		logger.Infof("connected to mongo")
 		return nil
 	}