Add nexus events

Sources/FirebladeECS/Nexus+SceneGraph.swift

@@ -15,14 +15,27 @@ extension Nexus {
             let (isNewMember, _) = parentChildrenMap[parent.identifier]!.insert(child.identifier)
             inserted = isNewMember
         }
+        if inserted {
+            delegate?.nexusEvent(ChildAdded(parent: parent.identifier, child: child.identifier))
+        }
         return inserted
     }
 
     public final func removeChild(_ child: Entity, from parent: Entity) -> Bool {
-        return parentChildrenMap[parent.identifier]?.remove(child.identifier) != nil
+        return removeChild(child.identifier, from: parent.identifier)
+    }
+
+    @discardableResult
+    public final func removeChild(_ child: EntityIdentifier, from parent: EntityIdentifier) -> Bool {
+        let removed: Bool = parentChildrenMap[parent]?.remove(child) != nil
+        if removed {
+            delegate?.nexusEvent(ChildRemoved(parent: parent, child: child))
+        }
+        return removed
     }
 
     public final func removeAllChildren(from parent: Entity) {
+        parentChildrenMap[parent.identifier]?.forEach { removeChild($0, from: parent.identifier) }
         return parentChildrenMap[parent.identifier] = nil
     }
 

Sources/FirebladeECS/NexusEvents.swift

@@ -46,3 +46,13 @@ public struct FamilyCreated: NexusEvent {
 public struct FamilyDestroyed: NexusEvent {
     public let family: FamilyTraitSet
 }
+
+public struct ChildAdded: NexusEvent {
+    public let parent: EntityIdentifier
+    public let child: EntityIdentifier
+}
+
+public struct ChildRemoved: NexusEvent {
+    public let parent: EntityIdentifier
+    public let child: EntityIdentifier
+}