test_runner: add [Symbol.dispose] to mock Timeout class

[HttpGetBinary]

Summary

Fixes #62815

The Timeout object returned by MockTimers was missing [Symbol.dispose], which means code using the using keyword with setTimeout would throw when mock timers are active.

Fix

Added [Symbol.dispose]() to the Timeout class in mock_timers.js. It calls globalThis.clearTimeout(this), which — when mocks are active — routes to the mock's own #clearTimeout, matching real Timeout behavior.

Test

// Should not throw
const t = mock.timers.enable({ apis: ['setTimeout'] });
{
  using timer = setTimeout(() => {}, 1000);
} // [Symbol.dispose] called here

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[Renegade334]

Please don't submit PRs against issues that already have open, active PRs.