Use same pattern as in metrics_acsl.ml.

The final computation state [Computed] or [Aborted] is set by [compute_function],
before calling the function [post_analysis] of domains, as those may use
plugins that use Eva results.

Removes optional argument [access] from [as_zone].

New function [as_cvalue_result] returns error cases without conversion.

New function [get_cvalue_model_result] returns the error cases without
conversion.

Nonterm: uses List.iter and Eva.Results.callstacks instead of iter_callstacks.

Removes [get_kinstr_state].
Uses these new functions in Results, to be more consistent.