Idea: support virtual table of LAPACK functions #413
Description
This might more properly belong in lapack-sys, but it would be very useful to be able to reuse BLAS and LAPACK from SciPy when using lax and ndarray-linalg to build Python extension modules with PyO3.
SciPy exposes routines from the BLAS and LAPACK it was linked against in a manner that can be imported with Cython's cimport, in the modules scipy.linalg.cython_blas and scipy.linalg.cython_lapack, to allow other Python extension modules implemented using Cython to reuse BLAS and LAPACK instead of needing to supply their own copy. I am not sure the best way to identify and properly link against these functions; I have one working method at lenskit/lkpy#960, fishing a pointer to sposv out of Python at runtime (the Cython modules expose them in a Python dictionary).
I imagine an interface where a PyO3 extension module can do something like use lax with a python feature, then call a method like lax::init_from_python(py) in a module initializer to grab the proper function pointers and set them up for lax to use, after which the lax methods (and therefore ndarray-linalg) will work without needing to compile or link against a separate BLAS and LAPACK.
In shared-library settings, like Pixi/Conda or system packages, all of the different modules can directly link against the same "system" BLAS. However, Python binary wheels do not make that easy, and the general solution is for each package to statically link against BLAS, or to use SciPy's export if it depends on SciPy.