FIX abstract classes in BaseObjective

[tomMoral]

This fixes the fact that BaseObjective was not raising error if an abstractmethod is not implemented.
It also makes the backward compatibility between compute/evaluate_result work with results that are dictionaries.

Finally, it renames Objective.get_one_solution into Objective.get_one_result.

[codecov-commenter]

Codecov Report

Merging #631 (1cb0b2c) into main (c689d24) will increase coverage by 0.64%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #631      +/-   ##
==========================================
+ Coverage   55.08%   55.73%   +0.64%     
==========================================
  Files          44       44              
  Lines        2861     2869       +8     
  Branches      527      528       +1     
==========================================
+ Hits         1576     1599      +23     
+ Misses       1167     1153      -14     
+ Partials      118      117       -1