Make `MAP` and `TNS` atomic.

[python-processing-unit]

According to the specification section 3:

MAP and TNS values are reference (aliasing) types: assigning a MAP or TNS to another identifier copies a reference to the same underlying container rather than performing an implicit deep copy. Mutating a map (via map<...> = ..., DEL, or other mutating operators) or mutating a tensor element through indexed assignment will be observed through any other identifier that references the same container. Use the built-in COPY (shallow copy) or DEEPCOPY (recursive deep copy) operators when a non-aliased duplicate is REQUIRED.

This MUST be changed, with MAP and TNS becoming atomic (de-referenced) types like the other types.

Update both the implementation and the specification.