Implement matrix assembly and factorization persistent through entire simulation

[jibril-b-coulibaly]

Assemble and factorize direct solver matrices only once at the beginning of the first step

corresponding issue: #566

[rserban]

I strongly suggest you ask us first before starting work on a new PR.
In particular, this type of feature has been on my todo list for a while and I intend to implement it in the near future. Having said that, I will implement something more robust and general than what you proposed, where the Jacobian is evaluated and factorized when needed and reused over multiple steps as long as it's still appropriate.

[jibril-b-coulibaly]

@rserban as I clarified in #566 , this is something I discussed with @tasora @dariofusai93 @dariomangoni .

I thought they might be in charge of triage for this PR/issue, and that maybe you had talked about it without me as well.

Let's find a way forward together