feat: add protected handler support and rename command to pushNotificationName

- Add protected flag to RegisterHandler methods across all types
- Protected handlers cannot be unregistered, UnregisterHandler returns error
- Rename 'command' parameter to 'pushNotificationName' for clarity
- Update PushNotificationInfo.Command field to Name field
- Add comprehensive test for protected handler functionality
- Update all existing tests to use new protected parameter (false by default)
- Improve error messages to use 'push notification' terminology

Benefits:
- Critical handlers can be protected from accidental unregistration
- Clearer naming reflects that these are notification names, not commands
- Better error handling with informative error messages
- Backward compatible (existing handlers work with protected=false)

redis.go

@@ -824,11 +824,12 @@ func (c *Client) initializePushProcessor() {
 	}
 }
 
-// RegisterPushNotificationHandler registers a handler for a specific push notification command.
-// Returns an error if a handler is already registered for this command.
-func (c *Client) RegisterPushNotificationHandler(command string, handler PushNotificationHandler) error {
+// RegisterPushNotificationHandler registers a handler for a specific push notification name.
+// Returns an error if a handler is already registered for this push notification name.
+// If protected is true, the handler cannot be unregistered.
+func (c *Client) RegisterPushNotificationHandler(pushNotificationName string, handler PushNotificationHandler, protected bool) error {
 	if c.pushProcessor != nil {
-		return c.pushProcessor.RegisterHandler(command, handler)
+		return c.pushProcessor.RegisterHandler(pushNotificationName, handler, protected)
 	}
 	return nil
 }
@@ -996,11 +997,12 @@ func (c *Conn) Process(ctx context.Context, cmd Cmder) error {
 	return err
 }
 
-// RegisterPushNotificationHandler registers a handler for a specific push notification command.
-// Returns an error if a handler is already registered for this command.
-func (c *Conn) RegisterPushNotificationHandler(command string, handler PushNotificationHandler) error {
+// RegisterPushNotificationHandler registers a handler for a specific push notification name.
+// Returns an error if a handler is already registered for this push notification name.
+// If protected is true, the handler cannot be unregistered.
+func (c *Conn) RegisterPushNotificationHandler(pushNotificationName string, handler PushNotificationHandler, protected bool) error {
 	if c.pushProcessor != nil {
-		return c.pushProcessor.RegisterHandler(command, handler)
+		return c.pushProcessor.RegisterHandler(pushNotificationName, handler, protected)
 	}
 	return nil
 }