Source distribution should bootstrap CMake

[ghost]

CMake allows bootstrapping from source (with just autotools/GNU Make). Because this package is often the only method to get a new CMake with just pip available, I think it would be too difficult to add logic that would bootstrap a release CMake before calling scikit-build if CMake wasn't found on the path.

This would essentially be:

if is_unix and not which('cmake'):
    download_extract('cmake.tar.gz')
    run('./bootstrap --prefix={prefix} && make && make install')
    os.environ['PATH'] += '{prefix}'

[minrk]

I looked into this a bit, and I think it needs special handling logic in scikit-build-core, because this package itself uses scikit-build-core, which then assumes cmake is on the system when it builds this package. If there were an override for cmake_executable or something, this package could provide a wrapper script to bootstrap and then call its own cmake, I think. I struggle a bit with understanding the chicken and egg sequence, though.