PyPy support

[fohrloop]

Tested wakepy on PyPy 7.3.11 (Python 3.9.16) and it seemed to work fine on Ubuntu. This would require a bit more testing as for example on Windows wakepy uses ctypes which has it's own implementation on PyPy. Also it's not currently possible to install wakepy for development or run unit tests, as the tests use time-machine which supports only CPython.

Task:

• Check if could get rid of time-machine in tests (or use some other library on PyPy)
• Check if there are other obstacles for using wakepy on PyPy. If so, remove them.
• Test wakepy on Windows + PyPy. Does it work?
• Check that unit tests test things that would crash loudly if an another implementation of Python (e.g. PyPy) would not be supported
• Add tests in pipelines and tox for PyPy versions
• Update docs for PyPy support