move runtime entity ID counter from EntityFactory back to Entity

EntityFactory is specialized for the purpose of deserializing data from worlds, and runtime ID assignment isn't related.

src/entity/Entity.php

@@ -77,6 +77,16 @@ abstract class Entity{
 
 	public const MOTION_THRESHOLD = 0.00001;
 
+	/** @var int */
+	private static $entityCount = 1;
+
+	/**
+	 * Returns a new runtime entity ID for a new entity.
+	 */
+	public static function nextRuntimeId() : int{
+		return self::$entityCount++;
+	}
+
 	/** @var Player[] */
 	protected $hasSpawned = [];
 
@@ -221,7 +231,7 @@ abstract class Entity{
 			$this->eyeHeight = $this->height / 2 + 0.1;
 		}
 
-		$this->id = EntityFactory::nextRuntimeId();
+		$this->id = self::nextRuntimeId();
 		$this->server = $location->getWorldNonNull()->getServer();
 
 		$this->location = $location->asLocation();

src/entity/EntityFactory.php

@@ -65,9 +65,6 @@ use function reset;
 final class EntityFactory{
 	use SingletonTrait;
 
-	/** @var int */
-	private static $entityCount = 1;
-
 	/**
 	 * @var \Closure[] base class => creator function
 	 * @phpstan-var array<class-string<Entity>, \Closure(World, CompoundTag) : Entity>
@@ -223,13 +220,6 @@ final class EntityFactory{
 		$this->saveNames[$className] = $saveNames;
 	}
 
-	/**
-	 * Returns a new runtime entity ID for a new entity.
-	 */
-	public static function nextRuntimeId() : int{
-		return self::$entityCount++;
-	}
-
 	/**
 	 * Creates an entity from data stored on a chunk.
 	 *