feat(core): event queue, Ethernet, switch, ARP, IPv4, ICMP, routing and firewall

First slice of the TypeScript port of the filius-ipad runtime engine,
with 29 tests ported from the Swift suite. Parts not ported yet throw
NotPortedError instead of guessing.

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

packages/core/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "@mdg-filius/core",
+  "version": "0.0.0",
+  "private": true,
+  "license": "GPL-3.0-only",
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts"
+  }
+}