Add Land Niederer Active Stress Model for Electromechanics

[kko27]

Current situation

Implements #606, the Land Niederer active stress model for coupled electromechanics. The phenomenological model consists of 7 state variables that describe the unbound, pre-power and post-power stroke states, the Calcium-Troponin binding kinetics, and the cross-bridge distortions. Length-dependency is embedded in the equations as well as the final active tension computation which collects several state variables together.

Note: this PR is currently in a draft stage, waiting on the merging of PR #650.

Release Notes

• Adds the Land-Niederer active-stress ODE model
• Adds the model XML parameters and MPI parameter distribution
• Includes coupled electromechanics slab regression test that uses the Land-Niederer contraction model
• Includes unit test to test the implementation of the Land-Niederer ODE model

Documentation

The Land Niederer active stress class has been given detailed Doxygen documentation. At a certain point, we should definitely add a user-guide style documentation for electromechanics akin to how electrophysiology ionic models are described in our documentation page.

Testing

A unit test following the twitch protocol described in ./tests/unitTests/active_stress_tests was created. A CI test using the same slab mesh files has also been included.

Code of Conduct & Contributing Guidelines

• I agree to follow the Code of Conduct and Contributing Guidelines.

[codecov]

Codecov Report

❌ Patch coverage is 99.33775% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 73.53%. Comparing base (c9838bd) to head (5ecc006).

Files with missing lines	Patch %	Lines
Code/Source/solver/ActiveStressLandNiederer.h	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #652      +/-   ##
==========================================
+ Coverage   73.41%   73.53%   +0.12%     
==========================================
  Files         269      272       +3     
  Lines       40337    40489     +152     
  Branches     6755     6759       +4     
==========================================
+ Hits        29612    29775     +163     
+ Misses      10482    10470      -12     
- Partials      243      244       +1     

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