refactor execution handling and add missing validation checks

src/main/resources/assets/knockedback/lang/en_us.json

@@ -4,6 +4,7 @@
   "key.categories.knockedback": "Knockedback Controls",
   "message.knockedback.cannot_carry_while_knocked": "You cannot carry others while you are knocked!",
   "message.knockedback.cannot_execute_while_knocked": "You cannot execute others while you are knocked!",
+  "message.knockedback.cannot_execute_carried_player": "You cannot execute a player who is being carried!",
   "message.knockedback.picked_up": "Picked up %s",
   "message.knockedback.being_carried": "You are being carried by %s",
   "message.knockedback.dropped": "Dropped %s",
@@ -16,4 +17,4 @@
   "message.knockedback.you_were_executed": "You were executed by %s!",
   "overlay.knockedback.recovery_time": "Time until recovery: %s s",
   "death.attack.knockedback_execution": "%1$s was executed mercilessly."
-}
+}