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/src/runtime/speed.ts

@@ -0,0 +1,33 @@
+// Ported from filius-ipad (GPLv2/GPLv3):
+//   State/TopologyNetworkRuntimeEngine.swift (TopologyNetworkRuntimeSpeed)
+// Java counterpart: filius.hardware.Verbindung (MIN_VERZOEGERUNG_IN_MILLIS,
+//   verzoegerungsFaktor) and GUIMainMenu.updateLatency.
+
+export const MINIMUM_SPEED_PERCENT = 1;
+export const MAXIMUM_SPEED_PERCENT = 100;
+export const DEFAULT_SPEED_PERCENT = 90;
+export const JAVA_MINIMUM_LINK_DELAY_MILLISECONDS = 5;
+
+export class RuntimeSpeed {
+  readonly percent: number;
+
+  constructor(percent: number = DEFAULT_SPEED_PERCENT) {
+    this.percent = Math.min(MAXIMUM_SPEED_PERCENT, Math.max(MINIMUM_SPEED_PERCENT, Math.trunc(percent)));
+  }
+
+  /** Java's delay factor: 1 at full speed, 100 at the slowest. */
+  get javaDelayFactor(): number {
+    return MAXIMUM_SPEED_PERCENT - this.percent + 1;
+  }
+
+  /** How long a frame travels over one cable. */
+  get linkTransmissionDelayMilliseconds(): number {
+    return JAVA_MINIMUM_LINK_DELAY_MILLISECONDS * this.javaDelayFactor;
+  }
+
+  /** A base delay scaled like a cable, or undefined past the safe integer range. */
+  scaledLinkDelay(baseMilliseconds: number): number | undefined {
+    const delay = baseMilliseconds * this.javaDelayFactor;
+    return Number.isSafeInteger(delay) ? delay : undefined;
+  }
+}