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* fix popcount64 name conflict on NetBSD, 189
* even though PyPy is not actively supported, allow running tests for
PyPy 3.7 and 3.8, see also 188
* allow running `python setup.py test`
* add official Python 3.12 support
* simplify count functionality in util module
* retire `bitcount_lookup[256]` table
* improve `util.count_n()` error messages
* avoid `util` module tests from being run more than once in each
call to `bitarray.test()` when called multiple times in the same
Python process, see 6e52e49a
* improve testing