Add support for initializing effect in MergedEffect (#182)

Author: ra1028

Sources/Atoms/Effect/MergedEffect.swift

@@ -2,12 +2,16 @@
 // MergedEffect<each Effect: AtomEffect>
 /// An atom effect that merges multiple atom effects into one.
 public struct MergedEffect: AtomEffect {
+    private let initializing: @MainActor (Context) -> Void
     private let initialized: @MainActor (Context) -> Void
     private let updated: @MainActor (Context) -> Void
     private let released: @MainActor (Context) -> Void
 
     /// Creates an atom effect that merges multiple atom effects into one.
     public init<each Effect: AtomEffect>(_ effect: repeat each Effect) {
+        initializing = { @Sendable context in
+            repeat (each effect).initializing(context: context)
+        }
         initialized = { @Sendable context in
             repeat (each effect).initialized(context: context)
         }
@@ -19,8 +23,14 @@ public struct MergedEffect: AtomEffect {
         }
     }
 
-    /// A lifecycle event that is triggered when the atom is first used and initialized,
-    /// or once it is released and re-initialized again.
+    /// A lifecycle event that is triggered before the atom is first used and initialized,
+    /// or once it is released and re-initialized.
+    public func initializing(context: Context) {
+        initializing(context)
+    }
+
+    /// A lifecycle event that is triggered after the atom is first used and initialized,
+    /// or once it is released and re-initialized.
     public func initialized(context: Context) {
         initialized(context)
     }