
Issues were: * Abusing of `WITH_PYTHON_INSTALL_NUMPY` by both Audaspace and Mantaflow. - `PYTHON_INSTALL` options only decide whether we copy python (and some extra modules) in our Blender installation. On linux it makes much more sense to use global python installation. - Now we have instead a proper `WITH_PYTHON_NUMPY` * Bad assumptions regarding path of headers relative to path of python module. - In current Debian testing, modules are under `python3.9` directory, while headers are under `python3` directory. - Now we properly `find_path` for headers as well, modifying `find_python_package` to take an optional argument for headers. Note that the required changes done to `extern` libraries are in blender-specific files that do not exist upstream. Differential Revision: https://developer.blender.org/D9773
When updating a library remember to: * Update the README.blender with the corresponding version. * Update the THIRD-PARTY-LICENSE.txt document