CLN: use isnan() instead of the Py_IS_NAN macro
Since 3.11 the later is just an alias for isnan().  See also https://github.com/python/cpython/issues/119613

What about Python 3.10? Noted on the C99 requirement (we actually require a C11 compiler anyway) but are these macros equivalent still on 3.10 or is there a possibility of a behavior difference? There is.  If you support platforms without IEEE 754, without NaN, and without C99+ ``<math.h>``.  Macroses were more complex to cover such cases, e.g.:
https://github.com/python/cpython/blob/c8f868dc52f98011d0f9b459b6487920bfb0ac4d/Include/pymath.h#L97-L103 OK thanks for that info. I think we are OK with this as is then. Appreciate the PR @mroeschke  Thanks @skirpichev 