fix: add Vitest fake timer detection to asyncWrapper

[penkzhou]

What: Add Vitest fake timer detection to the asyncWrapper in pure.js, so that waitFor (and by extension user.click via @testing-library/user-event) no longer hangs when Vitest fake timers are active.

Why: The asyncWrapper uses setTimeout(0) to drain the microtask queue after a callback completes. When fake timers are active, this setTimeout never fires unless the test framework advances timers. The existing code only checks for Jest fake timers (via the jest global), so Vitest users with vi.useFakeTimers() experience indefinite hangs in waitFor and user.click. This is the root cause of #1197 and relates to #1187.

How:

• Added vitestFakeTimersAreEnabled() — checks for the vi global AND setTimeout.clock (set by @sinonjs/fake-timers, which Vitest uses internally). Both conditions must be true to avoid false positives when Vitest is present but real timers are in use.
• Extracted advanceFakeTimers() — a unified helper that tries Jest first, then Vitest, keeping the asyncWrapper itself clean.
• The asyncWrapper's setTimeout(0) + advance pattern is unchanged; only the detection scope is widened.
• Added regression tests covering Jest legacy/modern fake timers, real timers, and fake timer detection logic (unit-level assertions on setTimeout.clock and _isMockFunction presence).

Note: The Vitest code path cannot be fully integration-tested within Jest (since jest is always available as a global and takes priority in detection). The detection logic is verified via unit tests that assert the signals each framework sets on setTimeout. Full Vitest integration was verified manually in a separate Vitest project.

Checklist:

• Documentation added to the docs site (N/A — internal detection logic, no API change)
• Tests
• TypeScript definitions updated (N/A — no public API change)
• Ready to be merged

Closes #1197
Relates to #1187

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 8a926ae:

Sandbox	Source
react-testing-library-examples	Configuration

[penkzhou]

I encountered this leak during development. Since the source of the leak is within this specific library, I would like to have it fixed so that more people can benefit from the solution. cc @eps1lon @MichaelDeBoey