Precise Fortran value model.

Note that we actually think about two different models: one storing values "machine-like" (Machine), one storing them "mathematically idealized" (Idealized). Only certain Fortran types have these split representations, namely integers and logicals. The rest have a single representation each.

Both representations may be convenient in different own ways:

• Machine representation is efficient, and should retain common overflow behaviours without explicitly handling them.
• Idealized representation is easier to handle, and enables safe checking for overflows.

The same kind algebra is performed for both, so types & kinds should match.

As of 2022-08-15, idealized representation isn't properly supported -- this module simply re-exports the machine representation.