sample: ICMP ping utility

[benaadams]

Problem

ICMP is commonly used for ping, traceroute, and network diagnostics - good candidates for demonstrating the library end-to-end.

Sub-tasks

• Create sample/Magma.Icmp.Ping - raw ICMP ping utility
• Demonstrates full stack: Ethernet -> IP -> ICMP
• Works over AF_XDP (Linux) or WinTun (Windows)
• README with usage instructions

Dependencies

Depends on: #110, one of #120 or #117 (needs a working platform backend)
Unlocks: good demo / educational piece

Phase

Phase 3 (Advanced Integrations)