added code from unity

Runtime/IPopupAnimator.cs

@@ -0,0 +1,37 @@
+using System;
+using UnityEngine;
+
+namespace Jovian.PopupSystem {
+    /// <summary>
+    /// Interface for popup show/hide animations. Each registered category gets its own instance
+    /// to prevent state corruption during concurrent animations. Driven by float timers in
+    /// <see cref="Tick"/>, not coroutines.
+    /// </summary>
+    public interface IPopupAnimator {
+        /// <summary>
+        /// Begins a show animation on the given CanvasGroup. Typically fades alpha from 0 to 1.
+        /// </summary>
+        /// <param name="canvasGroup">The CanvasGroup to animate.</param>
+        /// <param name="duration">Animation duration in seconds.</param>
+        /// <param name="onComplete">Callback invoked when the animation finishes. May be null.</param>
+        void Show(CanvasGroup canvasGroup, float duration, Action onComplete);
+
+        /// <summary>
+        /// Begins a hide animation on the given CanvasGroup. Typically fades alpha to 0.
+        /// </summary>
+        /// <param name="canvasGroup">The CanvasGroup to animate.</param>
+        /// <param name="duration">Animation duration in seconds.</param>
+        /// <param name="onComplete">Callback invoked when the animation finishes. May be null.</param>
+        void Hide(CanvasGroup canvasGroup, float duration, Action onComplete);
+
+        /// <summary>
+        /// Advances the animation by deltaTime. Call every frame from <see cref="IPopupSystem.Tick"/>.
+        /// </summary>
+        void Tick(float deltaTime);
+
+        /// <summary>
+        /// True if an animation is currently in progress.
+        /// </summary>
+        bool IsAnimating { get; }
+    }
+}