devel/boost-python-libs: add NumPy support

numpy component is always built but runtime dependency is left out
until subpackaging to avoid always pulling py-numpy. Consumers should
add RUN_DEPENDS+=${PYNUMPY} instead to avoid the following:

ImportError: No module named numpy.core._multiarray_umath
ImportError: numpy.core._multiarray_umath failed to import

PR: 225589 238130