fix(probe): cast timeval fields to platform width (unblocks macOS/Windows build)

The setup-zig re-pin in the previous commit unmasked a pre-existing
cross-platform compile error that the broken action had hidden by failing
before the build ever ran. posix.timeval field widths vary by platform:

  - Linux:   sec/usec are i64       -> compiled (only passing OS)
  - Windows: sec/usec are c_long/i32 -> error: expected c_long, found i64 (.sec)
  - macOS:   sec i64, usec i32       -> error: expected i32, found i64 (.usec)

Assigning i64 locals only compiled on Linux. Inline @intcast into the
field initialisers so each value coerces to the platform field type.
The matrix only compiles on macOS/Windows (run-integration: false), so
this is sufficient for a green build; Winsock SO_RCVTIMEO runtime
semantics are unchanged and out of scope here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvsZgNxFbeqfRmrVFNhJ8G

Author: claude

src/interface/ffi/src/probe.zig

@@ -194,12 +194,12 @@ fn udpExchange(
     );
     defer posix.close(sock);
 
-    // set receive timeout
-    const timeout_sec: i64 = @intCast(timeout_ms / 1000);
-    const timeout_usec: i64 = @intCast(@as(u64, timeout_ms % 1000) * 1000);
+    // set receive timeout — cast into the timeval field types, whose width
+    // varies by platform: sec/usec are i64 on Linux, c_long (i32) on Windows,
+    // and i64/i32 (time_t/suseconds_t) on macOS. @intCast adapts to each.
     const tv = posix.timeval{
-        .sec = timeout_sec,
-        .usec = timeout_usec,
+        .sec = @intCast(timeout_ms / 1000),
+        .usec = @intCast(@as(u64, timeout_ms % 1000) * 1000),
     };
     try posix.setsockopt(sock, posix.SOL.SOCKET, posix.SO.RCVTIMEO, std.mem.asBytes(&tv));