Add Montgomery conversion and high level I/O

[minosgalanakis]

Description

This pr will be rebased on top of PR 6095 and PR 6083

Because it brings all the changes forward please disregard all the files, aside from the following

git diff df6170759..HEAD --name-status
M       library/bignum_mod.c
M       library/bignum_mod.h
M       library/bignum_mod_raw.c
M       library/bignum_mod_raw.h

Status

*IN DEVELOPMENT

Requires Backporting

NO

Additional comments

Any additional information that could be of interest

Todos

• [ ] Rebase as
• [ ] Tests