feat(core): UDP sockets in the simulation core

engine.ts ports the UDP part of Swift's "UDP sockets and Router RIP": a
socket bound to a given port or to a free one drawn from 49152–65534 with
Java's random numbers on Swift's seed; sending, also as a limited broadcast
on every interface (or the bound one) with TTL 1; delivery into the queue
of every socket on the destination port, which then answers to the last
sender; receiving, with a timeout that advances the virtual clock; closing.
Stopping forgets sockets and queues. RIP stays not ported; Swift's DHCP
handling of a datagram has nothing to do until DHCP is in the snapshot.

The oracle gets the steps bindUdp, sendUdp, receiveUdp and closeSocket on
both sides and reports the sockets. Two new scenarios — a LAN, and two
networks through a router with a UDP firewall rule and a broadcast that
does not cross it — match the Swift engine trace for trace, the random
ports included. Swift's four UDP engine tests are ported, with a test for
stopping. 11 mutation probes were all caught (one only after the stop test
was added).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/test/scenarios/firewall-and-loss.swift.json

@@ -80,6 +80,9 @@
       "packet" : 7,
       "type" : "delivered"
     }
+  ],
+  "sockets" : [
+
   ],
   "switchTables" : {
     "00000000-0000-0000-0000-000000000405" : {