Move pattern check to utils

Checking if the sparsity pattern of the indices and the weights matrices are the same is highly expensive from the computational point of view. Also, the check sometimes is not strictly necessary, especially when the matrices have been produced by talon itself.

This commit removes the check from the initialisation of linear operators. The check is still available as a separate function at talon.utils.check_pattern_iw.

The corresponding tests and documentation have been adapted.

Type hints have been added to the functions in the talon.utils module.

This MR solves #39 (closed) and partially addresses #25 .