Add a behavior tree to the enemy

Add the Beehave addon.
Make the enemy do the same thing as before but with a behavior tree.

addons/beehave/metrics/beehave_global_metrics.gd

@@ -0,0 +1,54 @@
+extends Node
+
+var _tree_count: int = 0
+var _active_tree_count: int = 0
+var _registered_trees: Array[BeehaveTree] = []
+
+
+func _enter_tree() -> void:
+	Performance.add_custom_monitor("beehave/total_trees", _get_total_trees)
+	Performance.add_custom_monitor("beehave/total_enabled_trees", _get_total_enabled_trees)
+
+
+func register_tree(tree: BeehaveTree) -> void:
+	if _registered_trees.has(tree):
+		return
+	
+	_registered_trees.append(tree)
+	_tree_count += 1
+	
+	if tree.enabled:
+		_active_tree_count += 1
+	
+	tree.tree_enabled.connect(_on_tree_enabled)
+	tree.tree_disabled.connect(_on_tree_disabled)
+
+
+func unregister_tree(tree: BeehaveTree) -> void:
+	if not _registered_trees.has(tree):
+		return
+	
+	_registered_trees.erase(tree)
+	_tree_count -= 1
+	
+	if tree.enabled:
+		_active_tree_count -= 1
+	
+	tree.tree_enabled.disconnect(_on_tree_enabled)
+	tree.tree_disabled.disconnect(_on_tree_disabled)
+
+
+func _get_total_trees() -> int:
+	return _tree_count
+
+	
+func _get_total_enabled_trees() -> int:
+	return _active_tree_count
+
+
+func _on_tree_enabled() -> void:
+	_active_tree_count += 1
+
+
+func _on_tree_disabled() -> void:
+	_active_tree_count -= 1