Refactor Provisioners and Committee

[herr-seppia]

Summary

Current implementation of committee creation requires Provisioners to be mutable. This lead to a lof of Arc<Mutex> here and there to handle the mutability.

However, creation of a committee from Provisioners should not change the struct itself. This seems to be a tech debt, since the mutability is only required for implementation details.

Changing this, will remove the need for update_elegibility_flag at every round

Possible solution design or implementation

Additional context