Make sure that a CupertinoRadio doesn't crash in 0x0 environment

[ahmedsameha1]

This is my attempt to handle #6537 for the CupertinoRadio widget.

[gemini-code-assist]

Code Review

This pull request adds a regression test to ensure CupertinoRadio doesn't crash when rendered in a zero-sized area. The added test is good, but it only covers the light mode, unselected, and disabled state. The original issue was likely related to gradients used in dark mode, so I've suggested expanding the test to cover dark mode and selected states to make it more robust and prevent future regressions in those cases.

[gemini-code-assist]

The added test is a good start, but it only covers the case of an unselected, disabled radio in light mode. The crash was likely related to drawing gradients, which happens in dark mode. To make this test more comprehensive and prevent future regressions, it should also cover dark mode for both selected and unselected states.

  testWidgets('CupertinoRadio does not crash at zero area', (WidgetTester tester) async {
    // Unselected, disabled, light mode.
    await tester.pumpWidget(
      const CupertinoApp(
        home: Center(child: SizedBox.shrink(child: CupertinoRadio<bool>(value: false))),
      ),
    );
    expect(tester.getSize(find.byType(CupertinoRadio<bool>)), Size.zero);

    // Unselected, disabled, dark mode.
    await tester.pumpWidget(
      const CupertinoApp(
        theme: CupertinoThemeData(brightness: Brightness.dark),
        home: Center(child: SizedBox.shrink(child: CupertinoRadio<bool>(value: false))),
      ),
    );
    expect(tester.getSize(find.byType(CupertinoRadio<bool>)), Size.zero);

    // Selected, disabled, dark mode.
    await tester.pumpWidget(
      const CupertinoApp(
        theme: CupertinoThemeData(brightness: Brightness.dark),
        home: Center(child: SizedBox.shrink(child: CupertinoRadio<bool>(value: false, groupValue: false))),
      ),
    );
    expect(tester.getSize(find.byType(CupertinoRadio<bool>)), Size.zero);
  });

[dkwingsmt]

Checklist:

• The test is in the correct file
• The test name goes “does not crash at zero area”
• The target widget is wrapped by Center (or is fullscreen)
• The target widget does not have an overlay, or the overlay is tested
• The target widget is expected to have a size of exactly Size.zero