fix: use timeout-loop sniff for Windows/Npcap compatibility

L2pcapListenSocket on Windows does not support 'stopper' kwarg.
Replace with timeout=1.0 polling loop that respects stop_event.

dhcpd/server.py

@@ -88,14 +88,21 @@ class DHCPd:
         bpf = "udp port 67 or udp port 68"
         log.info("Starting packet sniff on %s (BPF: %s)",
                  self.iface or "<default>", bpf)
+        # Use timeout loop: L2pcapListenSocket (Windows/Npcap) does NOT
+        # support the 'stopper' kwarg, so poll with short timeout instead.
         try:
-            sniff(
-                iface=self.iface,
-                filter=bpf,
-                prn=self._handle_packet,
-                stopper=lambda: self._stop_event.is_set(),
-                store=False,
-            )
+            while not self._stop_event.is_set():
+                packets = sniff(
+                    iface=self.iface,
+                    filter=bpf,
+                    count=100,       # cap per batch
+                    timeout=1.0,     # poll every ~1s
+                    store=False,
+                )
+                for pkt in packets:
+                    if self._stop_event.is_set():
+                        break
+                    self._handle_packet(pkt)
         except Exception as e:
             log.error("Sniffer died: %s", e)
         log.info("Sniffer thread exited.")