Improve DirectSolver class names

[julianlitz]

Renamed DirectSolver classes to make their purpose and implementation clearer:

• DirectSolverGive -> DirectSolver_COO_MUMPS_Give
• DirectSolverTake -> DirectSolver_COO_MUMPS_Take
• DirectSolverGiveCustomLU -> DirectSolver_CSR_LU_Give
• DirectSolverTakeCustomLU -> DirectSolver_CSR_LU_Take

These new names explicitly indicate:

• The matrix storage format (COO or CSR)
• The solver algorithm (MUMPS or LU)
• The stencil operation mode (Give or Take)

This change improves readability and helps developers quickly identify the solver type and behavior.

Merge Request - GuideLine Checklist

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• There is at least one issue associated with the pull request.
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• Tests for new functionality has been added
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Checks by code reviewer(s):

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• The ticket goals for each associated issue are reached or problems are clearly addressed (i.e., a new issue was introduced).
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• No large data files have been added to the repository. Maximum size for files should be of the order of KB not MB. In particular avoid adding of pdf, word, or other files that cannot be change-tracked correctly by git.

[codecov]

Codecov Report

❌ Patch coverage is 96.29630% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.67%. Comparing base (05c809e) to head (fe4579d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...tSolver/DirectSolver-CSR-LU-Give/matrixStencil.cpp	66.66%	1 Missing ⚠️
...tSolver/DirectSolver-CSR-LU-Take/matrixStencil.cpp	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #155   +/-   ##
=======================================
  Coverage   88.67%   88.67%           
=======================================
  Files          87       87           
  Lines        4982     4982           
=======================================
  Hits         4418     4418           
  Misses        564      564           

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