Add example to test GLib.Variant type issue

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This PR adds and improves examples to demonstrate the reported GLib.Variant type issues in #239. The changes focus on providing a clear test case for the reported typing problems with GLib.Variant usage in different contexts.

Changes

• Improved and restructured the glib-2-variant example to better demonstrate variant usage
• Added comprehensive test cases for:
  • Basic variant creation and usage
  • DBus signal emission with variants
  • Complex variant structures
  • Variant unpacking methods
• Added clear documentation and comments
• Ensured clean program termination

Testing

The example can be run with:

cd examples/glib-2-variant
yarn install
yarn start

Related Issues

• Fixes Issue with GLib Variant types #239 (GLib.Variant type compatibility issues)
• Demonstrates the reported type errors with:
  • DBusExportedObject.emit_signal() with variants
  • GSettings value assignment with variants

Notes

• The example is designed to reproduce the type errors in a minimal, self-contained environment
• All variant types that were reported as problematic are included in the test cases
• The code is structured to make it easy to test different variant scenarios