Gate Unix-only server targets for Windows checks

tests/hostile_network.rs

@@ -18,6 +18,7 @@
 //! Determinism: the relay's drop/reorder/dup behavior is driven by a fixed-seed
 //! PRNG and by explicit one-shot toggles, never by wall-clock timing, so the
 //! tests are reproducible and fast.
+#![cfg(unix)]
 #![allow(
     clippy::collapsible_if,
     clippy::explicit_counter_loop,

tests/integration_smoke.rs

@@ -1,3 +1,4 @@
+#![cfg(unix)]
 #![allow(clippy::collapsible_if)]
 
 use std::fs;