Migrate radio_list_tile example to RadioGroup (removes deprecated usage)

[cnaples79]

Summary

• Migrate radio_list_tile diagrams to use RadioGroup
• Remove deprecated groupValue/onChanged on Radio/RadioListTile
• Update custom examples to use RadioGroup.maybeOf for onTap

Details

• Wraps example columns with RadioGroup to manage selection state
• RadioListTile entries now specify only value/title as per new API
• LinkedLabelRadio and LabeledRadio updated:
  • LinkedLabelRadio: show radio + RichText without managing state
  • LabeledRadio: call RadioGroup.maybeOf(context)?.onChanged(value) on tap

This aligns with Flutter 3.32 radio API updates.

Fixes flutter/flutter#175355

[Piinks]

Hey @cnaples79 thanks for contributing. There is already a PR open which was linked in the source issue. I am going to defer to that one since it was sent in first: #259