Convert to csr_array (internally)

[zerothi]

Describe the issue

Since scipy 1.8 (released in May 2022), csr_array is the preferred sparse array constructor. We should aim towards using this version as a base.

However, there are some issues this will entail:

1. The eye, kron, diags are not implemented in scipy for csr_array. And aren't in 1.12 either. So we will have to work around this issue regardless.
2. We are not really using the matrix multiplication method of csr_matrix, so the changes should be rather minimal in this sense.