Add different Mechanical simulations

[PProfizi]

In coherence with the proposed pseudocode, this PR adds the different mechanical simulation classes:

• StaticMechanicalSimulation
• TransientMechanicalSimulation
• ModalMechanicalSimulation
• HarmonicMechanicalSimulation

A first few additions are made to enable future work.

[codecov[bot]]

Codecov Report

Merging #258 (6f8bcf7) into post_refactor (6194e5b) will increase coverage by 2.86%. The diff coverage is 88.09%.

@@                Coverage Diff                @@
##           post_refactor     #258      +/-   ##
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+ Coverage          74.89%   77.75%   +2.86%     
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  Files                 30       30              
  Lines               1665     1713      +48     
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+ Hits                1247     1332      +85     
+ Misses               418      381      -37