Add Thin Waist address validation utilities and integrate into echo example

- Add ``libp2p/utils/address_validation.py`` with dynamic interface discovery
- Implement ``get_available_interfaces()``, ``get_optimal_binding_address()``, and ``expand_wildcard_address()``
- Update echo example to use dynamic address discovery instead of hardcoded wildcard
- Add safe fallbacks for environments lacking Thin Waist support
- Temporarily disable IPv6 support due to libp2p handshake issues (TODO: re-enable when resolved)