Implement Stacey boundary condition

[SouzaEM]

This implementation includes:

• Stacey boundary condition itself
• Modification of field logger to also log functionals
• Evaluation of mechanical energies to evaluate the boundary condition
• Regression tests based on the mechanical energy
• Second order time discretization options for velocities (although they didn't improve performance)

[codecov]

Codecov Report

Attention: Patch coverage is 96.44670% with 7 lines in your changes missing coverage. Please review.

Project coverage is 84.31%. Comparing base (a701161) to head (83e95c4).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
spyro/solvers/elastic_wave/local_abc.py	92.63%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
+ Coverage   84.23%   84.31%   +0.08%     
==========================================
  Files          56       58       +2     
  Lines        3729     3902     +173     
==========================================
+ Hits         3141     3290     +149     
- Misses        588      612      +24     

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[Olender]

I really like what you did with the FieldLogger class. Since it has grown a bit and if you have time could you add documentation as well? I think later I will add, in another PR, a File class that writes to binary in cases were firedrake is installed without VTK.

[SouzaEM]

So let's open another PR to address the binary format, the documentation, and other new features.