feat(sim): F4.2 the sim protocol, the simulation room and LocalSimHost; M9 measured

packages/protocol holds the one list of /sim messages and checks every
field, naming what is wrong. packages/sim has the simulation room for F and
the web worker: the document's snapshot at start, the engine's clock on the
wall clock with Java's speed as cable delay, subscriptions to cable
activity, a card's new frames and a program's new window lines, capture and
clock kept over a stop, the command line as first action, a core failure
told to every client. LocalSimHost mirrors the document into the worker and
back without echo. M9 in Chromium: 17 examples give the same capture as in
Node, character for character; the room runs in a real worker.

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

packages/sim/src/worker.ts

@@ -0,0 +1,15 @@
+// The entry of the web worker that holds a LocalSimHost's room.
+
+import type { Port } from './channel.js';
+import { serveRoom } from './serveRoom.js';
+
+// The worker's scope, with what it is used for here (the package has no DOM types).
+declare const self: Port;
+declare function setInterval(handler: () => void, milliseconds: number): unknown;
+declare const performance: { now(): number };
+
+serveRoom(self, {
+  now: () => performance.now(),
+  seed: () => Math.floor(Math.random() * 2 ** 31),
+  every: (milliseconds, tick) => setInterval(tick, milliseconds),
+});