Resolve "Refactor toplevel REPL" ✨️

Closes #76 🐔️👍️
Approved-by: v-lafeychine <vincent.lafeychine@proton.me>
Approved-by: aalbert <augustin.albert@bleu-azure.fr>

🦀️🍰🦀️🍰🦀️🍰

* fix(proost): remove useless map_err in main routine

* fix(proost): add ResultProcess type alias

* chore(proost): make annoying clippy happy

* fix(proost): add String argument to FileError

* fix(proost): simplify error type

* chore(parser): rename Error field from 'loc' to 'location'