Should `utils_test.py` be considered public API?

We currently expose a number of functions and fixtures in `distributed.utils_test`. While I would consider these implementation details of our tests, and not part of any stable user-facing API, other projects, including `dask/dask` rely on them for their test suites (https://github.com/dask/dask/blob/ac74939697c328bd6456aa9fad7d9520328db6e5/dask/tests/test_distributed.py#L11-L14, #5300, #6775, https://github.com/dask/distributed/pull/6802#pullrequestreview-1052813812). This creates friction between the stability requirements of downstream users and our ability to adjust the contents of `utils_test` to fit our internal testing needs. For example, we cannot easily move functionality around without breaking things for downstream users (https://github.com/dask/distributed/pull/6802#pullrequestreview-1052813812).

This leads me to several questions:
**Should the contents of `utils_test.py` be considered part of the public API?**

If so:
* What guarantees are we willing to make around API stability?
* How do we want to test/enforce those?
* Which parts should be considered public API?
* For example, should we only expose context managers/functions, but not fixtures?

If not:
* How do we make this clear and discourage users from importing them?
* How do we deal with projects that already import them?