Fix xtensor-stack#323

Fix xtensor-stack#323 - again

Co-authored-by: Roy Kid <lijichen365@gmail.com>

It's a requirement for being adapted by std::reverse_iterator

xternsor-python is header only library, so prefer arch-independed paths
cmake.

References:
*
xtensor-stack/xtl@d877d94
*
xtensor-stack/xtensor@7738389

Co-authored-by: Johan Mabille <johan.mabille@gmail.com>

Co-authored-by: Johan Mabille <johan.mabille@gmail.com>

As mentioned in xtensor-stack#333, the test environment is currently broken due to
conda packaging changes for Python starting with version 3.15 which just
came out. This explicitly adds both `python` and `libpython` to the test
environment so that the text executables can be built.

The current CMake script that is used to find NumPy does not always work
for me, and sometimes causes problems on the different systems I build
on. Given we have recently updated the minimum CMake version and the
minimum pybind11 version, these changes now use the standard CMake tools
to find Python3 and NumPy, and makes the links with the standard CMake
targets. I specifically use Python3 in the CMake as the indicated
pybind11 version no longer supports Python 2.7.