Implement dot product for sparse matrices

[lisette-espin]

• use divide and conquer
• use parallel processes
• use hd5?

[lisette-espin]

try:

1. https://scikit-learn.org/stable/modules/generated/sklearn.utils.extmath.safe_sparse_dot.html
2. https://pypi.org/project/sparse-dot-topn/

[lisette-espin]

try as well CSC instead of CSR