Refactor miranda to narrow its scope

[RondeauG]

Description

As per discussions that we've had internally, some features of miranda will be moved to either xscen (i.e. miranda.decode & miranda.structure) or ouranos-data-catalog (for some specific workflows).

Once those changes have been made and that we're sure that everything works well, we should remove them from miranda.

See also #128, Ouranosinc/xscen#153, and https://github.com/orgs/Ouranosinc/projects/10