test_runner: align mock timeout api

Expose Timeout.close() and Timeout[Symbol.dispose]() from MockTimers.

This keeps fake setTimeout() handles aligned with the public
Timeout API so disposal-based patterns do not throw.

Add targeted coverage for Timeout.close() and
Timeout[Symbol.dispose]().

Author: Han5991

lib/internal/test_runner/mock/mock_timers.js

@@ -69,12 +69,15 @@ const TIMERS_DEFAULT_INTERVAL = {
 };
 
 class Timeout {
+  #clear;
+
   constructor(opts) {
     this.id = opts.id;
     this.callback = opts.callback;
     this.runAt = opts.runAt;
     this.interval = opts.interval;
     this.args = opts.args;
+    this.#clear = opts.clear;
   }
 
   hasRef() {
@@ -92,6 +95,15 @@ class Timeout {
   refresh() {
     return this;
   }
+
+  close() {
+    this.#clear(this);
+    return this;
+  }
+
+  [SymbolDispose]() {
+    this.#clear(this);
+  }
 }
 
 class MockTimers {
@@ -310,6 +322,7 @@ class MockTimers {
       runAt: this.#now + delay,
       interval: isInterval ? delay : undefined,
       args,
+      clear: this.#clearTimeout,
     };
 
     const timer = new Timeout(opts);

test/parallel/test-runner-mock-timers.js

@@ -266,6 +266,32 @@ describe('Mock Timers Test Suite', () => {
         assert.deepStrictEqual(fn.mock.calls[0].arguments, args);
       });
 
+      it('should expose Timeout.prototype[Symbol.dispose]', (t) => {
+        t.mock.timers.enable({ apis: ['setTimeout'] });
+        const fn = t.mock.fn();
+        const timeout = globalThis.setTimeout(fn, 2000);
+
+        assert.strictEqual(typeof timeout[Symbol.dispose], 'function');
+
+        timeout[Symbol.dispose]();
+        t.mock.timers.tick(2000);
+
+        assert.strictEqual(fn.mock.callCount(), 0);
+      });
+
+      it('should expose Timeout.prototype.close()', (t) => {
+        t.mock.timers.enable({ apis: ['setTimeout'] });
+        const fn = t.mock.fn();
+        const timeout = globalThis.setTimeout(fn, 2000);
+
+        assert.strictEqual(typeof timeout.close, 'function');
+        assert.strictEqual(timeout.close(), timeout);
+
+        t.mock.timers.tick(2000);
+
+        assert.strictEqual(fn.mock.callCount(), 0);
+      });
+
       it('should keep setTimeout working if timers are disabled', (t, done) => {
         const now = Date.now();
         const timeout = 2;