feat(p2p-testing): Add cross-platform build checks and improve error handling
Enhances the P2P testing infrastructure to ensure cross-platform compatibility and provide better error handling for common Docker issues. Changes: - Add error handling for Docker network and container conflicts in start-nodes.sh - Emphasize Earthly (containerized builds) for GLIBC compatibility across different host OS - Add comprehensive documentation about cross-platform build requirements - Update Dockerfile and docker-compose.yml with clear build instructions - Add troubleshooting section for GLIBC errors in README The scripts now detect and provide helpful error messages for: - Network subnet overlaps with existing Docker networks - Container name conflicts from previous runs - Guidance to use Earthly builds instead of local cargo builds This ensures the P2P testing environment works reliably across different development environments (Fedora, Ubuntu, macOS, etc.) by building binaries in a controlled container environment that matches the Docker runtime GLIBC version.