Changed to scipy.sparse.*_array

[zerothi]

This will be the preferred way of interacting with scipy sparse matrices.

However, they have the down-side of not allowing 1D slicing (in older versions). Only in scipy commit: 66ec33370c889e9c9acba320354b624ee258ee22 did this enter (in June 2024).

So for now, it has to be limited only, but with the latest scipy, it shouldn't be a problem.

• [x] Closes #902
• [x] Added tests for new/changed functions?
• [x] Documentation for functionality in docs/
• [x] Changes documented in changes/<pr-num>.<type>.rst