fix(screenshot): destroy late texture in CaptureCompositedAfterFrame callback

If the editor spin loop times out before ScreenshotCapturer's coroutine fires
the callback, the callback would still later assign the captured Texture2D to
the (now-dead) local result variable. The texture itself would never reach the
consumer's finally-block DestroyTexture, leaking a Unity object until the next
domain reload.

Track caller-returned state; if the callback runs after timeout, destroy the
incoming texture immediately instead of assigning it.

Flagged by CodeRabbit on the prior commit.

Author: KamilDev

MCPForUnity/Runtime/Helpers/ScreenshotUtility.cs

@@ -243,11 +243,24 @@ private static Texture2D CaptureCompositedAfterFrame(int superSize, int timeoutS
         {
             Texture2D result = null;
             bool done = false;
-            ScreenshotCapturer.Begin(superSize, tex => { result = tex; done = true; });
+            bool callerReturned = false;
+            ScreenshotCapturer.Begin(superSize, tex =>
+            {
+                // Late completion after the spin loop timed out: caller will never consume
+                // the texture, so destroy it here to avoid leaking a Unity object.
+                if (callerReturned)
+                {
+                    if (tex != null) DestroyTexture(tex);
+                    return;
+                }
+                result = tex;
+                done = true;
+            });
             for (int i = 0; i < timeoutSteps && !done; i++)
             {
                 UnityEditor.EditorApplication.Step();
             }
+            callerReturned = true;
             return result;
         }
 #endif