fix(ios): defer fit assignment until MTKView is ready in experimental backend

RiveUIView creates its MTKView lazily during the first layout pass.
Setting rive.fit immediately after creating the view had no effect
because the drawable didn't exist yet. Store the desired fit as
pendingFit and apply it in layoutSubviews once the MTKView is present.

Author: mfazekas

ios/new/RiveReactNativeView.swift

@@ -1,6 +1,7 @@
-@_spi(RiveExperimental) import RiveRuntime
+import RiveRuntime
 import NitroModules
 import UIKit
+import MetalKit
 
 enum ExperimentalBindData {
   case none
@@ -27,9 +28,23 @@ class RiveReactNativeView: UIView {
   private var isViewReady = false
   private var configTask: Task<Void, Never>?
   private var isPaused = false
+  private var pendingFit: RiveRuntime.Fit?
 
   var autoPlay: Bool = true
 
+  override func layoutSubviews() {
+    super.layoutSubviews()
+    applyPendingFitIfMTKViewReady()
+  }
+
+  // https://github.com/rive-app/rive-nitro-react-native/pull/231
+  private func applyPendingFitIfMTKViewReady() {
+    guard let fit = pendingFit, let rive = riveInstance,
+          riveUIView?.subviews.contains(where: { $0 is MTKView }) == true else { return }
+    rive.fit = fit
+    pendingFit = nil
+  }
+
   func awaitViewReady() async -> Bool {
     if !isViewReady {
       await withCheckedContinuation { continuation in
@@ -93,14 +108,9 @@ class RiveReactNativeView: UIView {
 
           RCTLog("[RiveReactNativeView] Rive instance created successfully")
           self.riveInstance = rive
-          RCTLog("[RiveReactNativeView] Setting up RiveUIView...")
           self.setupRiveUIView(with: rive)
-          RCTLog("[RiveReactNativeView] RiveUIView setup complete")
 
-          // Set fit after view is in the hierarchy — passing fit to
-          // the Rive() constructor breaks .layout mode because the
-          // MTKView drawable isn't ready yet at construction time.
-          rive.fit = config.fit
+          self.pendingFit = config.fit
 
           if config.autoPlay {
             self.isPaused = false