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 +28,26 @@ 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
 
+  // Workaround: RiveUIView creates its MTKView lazily during the first
+  // layout pass, so setting rive.fit immediately after creating the view
+  // has no effect — the drawable doesn't exist yet. We store the desired
+  // fit and apply it here once the MTKView is present.
+  // TODO: Remove once rive-ios handles this internally.
+  override func layoutSubviews() {
+    super.layoutSubviews()
+    if let fit = pendingFit, let rive = riveInstance {
+      let hasMTKView = riveUIView?.subviews.contains(where: { $0 is MTKView }) ?? false
+      if hasMTKView {
+        rive.fit = fit
+        pendingFit = nil
+      }
+    }
+  }
+
   func awaitViewReady() async -> Bool {
     if !isViewReady {
       await withCheckedContinuation { continuation in
@@ -93,14 +111,10 @@ 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
+          // Defer fit — see layoutSubviews() comment.
+          self.pendingFit = config.fit
 
           if config.autoPlay {
             self.isPaused = false