pyximport compatibility in py312

[mosesyhc]

All tests succeed with the following warnings:

`
=============================== warnings summary ===============================
../../../../.local/lib/python3.10/site-packages/pyximport/pyximport.py:51
/home/wild/.local/lib/python3.10/site-packages/pyximport/pyximport.py:51: DeprecationWarning: the imp module is deprecated in favour of importlib and slated for removal in Python 3.12; see the module's documentation for alternative uses
import imp

tests/test_emu_cal/test_cal_mh.py::test_cal_method1[input20-input30-priorphys_lin-XXXX-input60-expectation0]
tests/test_emu_cal/test_emu_init.py::test_method1[XXXX-expectation1]
tests/test_emu_cal/test_emu_param_str.py::test_repr[PCGPwM-expectation1]
tests/test_emu_cal/test_emu_param_str.py::test_repr[PCGPwImpute-expectation3]
tests/test_emu_cal/test_emu_param_str.py::test_repr[XXXX-expectation5]
:914: ImportWarning: PyxImporter.find_spec() not found; falling back to find_module()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

---------- coverage: platform linux, python 3.10.12-final-0 ----------
Coverage HTML written to dir cov_html

========== 193 passed, 19 deselected, 10 warnings in 92.24s (0:01:32) ==========
`

Originally posted by @wildsm in #118 (comment)