feat: core types, time, rng, model fetch

Co-Authored-By: Claude Haiku 5.5 <[email protected]>

tests/core/rng.test.ts

@@ -0,0 +1,10 @@
+import { test, expect } from "bun:test";
+import { createRng } from "../../src/core/rng.ts";
+
+test("rng deterministic", () => {
+  const a = createRng(42), b = createRng(42), c = createRng(43);
+  const sa = [a.next(), a.next(), a.next()];
+  expect([b.next(), b.next(), b.next()]).toEqual(sa);
+  expect(c.next()).not.toBe(sa[0]);
+  const r = createRng(1); for (let i = 0; i < 1000; i++) { const v = r.int(3, 5); expect(v >= 3 && v <= 5).toBe(true); }
+});

tests/core/time.test.ts

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+import { test, expect } from "bun:test";
+import { ticksToSeconds, secondsToTicks } from "../../src/core/time.ts";
+
+test("ticks/seconds", () => {
+  expect(ticksToSeconds(960, 60)).toBeCloseTo(1);
+  expect(ticksToSeconds(3840, 120)).toBeCloseTo(2);
+  expect(secondsToTicks(0.5, 120)).toBeCloseTo(960);
+});