Some refactor in Radium crate

This refactor should go through many small steps to make sure that the whole process is merged.

In this branch, multiple attempt and proof-of-concept has been done:

• Use derive_more for Display for no-or-few logic fmt functions
• Use indoc for bigger blocks
• Use radium to do the .to_string() logic

In addition, the overall process is to make the radium crate with almost no dependencies to other RefinedRust crates, and to make it as small as possible, since radium should only contain logic for the Coq proof assistant:

• A RefCell<Option<T>> from radium changed to a simpler type, and the logic is now reflected by a OnceCell in translation:
  • Done with AbstractStructUse: RefCell<Option<AbstractStruct>> to Option<AbstractStruct>
  • Done with AbstractEnumUse: RefCell<Option<AbstractEnum>> to AbstractEnum
• The dependency of rrconfig got removed