Problem

The existing WinTun sample uses the old TAP-Windows path. Update it and measure the improvement.

Sub-tasks

• Update sample/Magma.WinTun.TcpHost to use native transport
• Add benchmark: TAP-Windows FileStream vs native ring buffer (packets/sec, latency percentiles)
• Document migration steps in a MIGRATION.md or in the sample README

Dependencies

Depends on: #116, #113 (benchmark infrastructure)
Unlocks: platform I/O benchmarks (#TBD)

Phase

Phase 2 (Platform Backends & Samples)