feat: Windows GUI development with egui - simple notepad example

- Fixed EguiBox Send+Sync trait bounds for thread safety
- Added missing Arc import for EguiBox implementation
- Simplified font setup in Windows notepad example
- Successfully built 4.5MB Windows GUI executable
- Nyash can now create native Windows desktop applications! 🎉

local_tests/test_windows_basic.nyash

@@ -0,0 +1,13 @@
+// 最もシンプルなWindowsテスト
+print("Hello Windows!")
+print("1 + 1 = " + (1 + 1))
+print("Nyash is running!")
+
+// ループテスト
+local i = 0
+loop(i < 3) {
+    print("Count: " + i)
+    i = i + 1
+}
+
+print("Done!")