Backend: reevaluate minimum CPython target

Currently, the C extensions are built targeting Python 3.7. Most of our dependencies do not support it (Python 3.7) at all, but our extensions are fully compatible with the latest CPython releases.

Is there any benefit, especially performance-wise, if we raise the minimum to CPython 3.11, mirroring NumPy's policy?

There's also the manylinux2014 topic. I think we could drop it at this point, maybe adding musllinux_1_2 in the process.