Migrate from Mocha/Chai/Sinon to Node built-in test runner

Replace mocha, chai, and sinon with node:test and node:assert/strict
(built into Node 22). This removes 3 dev dependencies while keeping
identical test coverage (438 pass, 44 skipped).

- Convert all fs.readFile callbacks to fs.readFileSync
- Replace sinon.spy() with mock.fn() from node:test
- Replace this.timeout() with { timeout } options on describe
- Replace this.skip() with test context t.skip()

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bfirsh

package-lock.json

@@ -14,20 +14,17 @@
   "scripts": {
     "build": "webpack",
     "typecheck": "tsc --noEmit",
-    "test": "npm run typecheck && prettier --check src/**/*.js && mocha ./test/*.spec.js",
-    "test:watch": "mocha -w ./test/*.spec.js",
+    "test": "npm run typecheck && prettier --check src/**/*.js && node --test ./test/*.spec.js",
+    "test:watch": "node --test --watch ./test/*.spec.js",
     "prepublish": "npm run build",
     "format": "prettier --write src/**/*.js"
   },
   "devDependencies": {
     "@types/node": "^25.0.2",
-    "chai": "^6.2.2",
     "eslint": "^9.15.0",
     "eslint-config-prettier": "^10.1.8",
     "eslint-webpack-plugin": "^5.0.2",
-    "mocha": "^11.7.1",
     "prettier": "^3.6.2",
-    "sinon": "^21.0.0",
     "terser-webpack-plugin": "^5.3.10",
     "typescript": "^5.8.3",
     "webpack": "^5.100.2",

package.json

@@ -1,4 +1,5 @@
-import { assert } from "chai";
+import assert from "node:assert/strict";
+import { describe, it, before, after } from "node:test";
 import fs from "fs";
 import NES from "../src/nes.js";
 import Controller from "../src/controller.js";
@@ -419,17 +420,12 @@ function formatResult(value) {
   );
 }
 
-describe("AccuracyCoin", function () {
-  this.timeout(600000); // 10 minutes — running 134 tests takes a while
-
+describe("AccuracyCoin", { timeout: 600000 }, function () {
   let run;
 
-  before(function (done) {
-    fs.readFile("roms/AccuracyCoin/AccuracyCoin.nes", function (err, data) {
-      if (err) return done(err);
-      run = runAccuracyCoin(data.toString("binary"));
-      done();
-    });
+  before(function () {
+    let data = fs.readFileSync("roms/AccuracyCoin/AccuracyCoin.nes");
+    run = runAccuracyCoin(data.toString("binary"));
   });
 
   it("should not crash before completing all tests", function () {
@@ -479,10 +475,11 @@ describe("AccuracyCoin", function () {
           it.skip(test.name + " — " + knownFailure, function () {});
           return;
         }
-        it(test.name, function () {
+        it(test.name, function (t) {
           let result = run.results[test.addr];
           if (result === 0x00) {
-            this.skip(); // not run (likely due to earlier crash)
+            t.skip(); // not run (likely due to earlier crash)
+            return;
           }
           if (!isPass(result)) {
             assert.fail(