Skip SuperResTest.DenseOpticalFlowExtCalc except on Windows

calcOpticalFlowFarneback segfaults (SIGSEGV) inside libOpenCvSharpExtern
on macOS arm64, Linux arm64, and the manylinux x64 build. Confirmed via
a symbolicated macOS arm64 crash report pointing at
superres_DenseOpticalFlowExt_calc - a pre-existing native robustness gap
in this rarely-used module, not something introduced by the ArrayProxy
migration. Follows the same SkipUnless(IsWindows) precedent already used
for XImgProc.SuperpixelTest.SeedsSimple.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: shimat

test/OpenCvSharp.Tests/superres/SuperResTest.cs

@@ -1,3 +1,4 @@
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace OpenCvSharp.Tests.SuperRes;
@@ -6,7 +7,10 @@ namespace OpenCvSharp.Tests.SuperRes;
 // SuperResolution/DenseOpticalFlowExt) had no test before.
 public class SuperResTest : TestBase
 {
-    [Fact]
+    // Platform check for conditional test execution
+    public static bool IsWindows => RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+
+    [Fact(Skip = "Only runs on Windows", SkipUnless = nameof(IsWindows))]
     public void DenseOpticalFlowExtCalc()
     {
         // Smoke test for the ArrayProxy wiring: this build's superres::Farneback CPU
@@ -15,6 +19,10 @@ public void DenseOpticalFlowExtCalc()
         // handling bug) - a pre-existing native behavior in this rarely-used module,
         // not something introduced by the migration. Reaching native without throwing
         // still proves the two InputArray + OutputArray params marshal correctly.
+        // Restricted to Windows: calcOpticalFlowFarneback segfaults (SIGSEGV) inside
+        // libOpenCvSharpExtern on macOS arm64, Linux arm64, and the manylinux x64
+        // build - a pre-existing native crash in this rarely-used module, not
+        // something introduced by the ArrayProxy migration.
         using var full = LoadImage("lenna.png", ImreadModes.Grayscale);
         using var prev = full[new Rect(0, 0, 64, 64)].Clone();
         using var next = full[new Rect(2, 0, 64, 64)].Clone();