docs: def extensions():
      """Returns list of `cython` extensions for `lazy_cythonize`."""
      import numpy
      from Cython.Build import cythonize
      ext = [
              Extension('phydmslib.numutils', ['phydmslib/numutils.pyx'],
                      include_dirs=[numpy.get_include()],
                      extra_compile_args=['-Wno-unused-function']),
            ]      
      return cythonize(ext)