[WIP] Fix multigrid agglomeration

[bigfooted]

Proposed Changes

Give a brief overview of your contribution here in a few sentences.

Implement multigrid agglomeration according to Nishikawa and Diskin.

• euler walls are working correctly.

• mpi still needs to be checked.

• I am submitting my contribution to the develop branch.

• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).

• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).

• I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.

• I have added a test case that demonstrates my contribution, if necessary.

• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.

In general, to fix commented‑out code, either remove it entirely or reinstate it as active code, and rely on version control history if you ever need to recover old implementations. If the intent is to document behavior, rewrite it as an explanatory comment rather than a compilable snippet.

For this case, the best fix without changing existing functionality is to delete the commented‑out declaration of factor on line 649. The active implementation already sets factor via base_damp, so removing the old, commented line will not alter behavior. No new methods, imports, or definitions are required; only the single line within CMultiGridIntegration::SetProlongated_Correction in SU2_CFD/src/integration/CMultiGridIntegration.cpp needs to be removed.

[bigfooted]

When MG is finalized, these will be initial values and will be adaptively changed.

To fix the problem, we should eliminate the commented-out code while keeping the current behavior (Coeff equal to 1.1) unchanged. Since the comment above already hints that the CFL strategy “should be rewritten to use adaptive CFL,” we can either (a) delete the commented pow(...) call entirely, or (b) turn it into a clearer descriptive comment that does not look like disabled code. The minimal, safest change is to remove the commented pow(...) expression, leaving the constant assignment as-is.

Concretely, in Common/src/geometry/CMultiGridGeometry.cpp, in the block around lines 718–724, we will modify the line

722:     const su2double Coeff = 1.1; //pow(su2double(Global_nPointFine) / Global_nPointCoarse, 1.0 / nDim);

to remove the commented-out code. We can either leave just the numeric assignment or replace the trailing comment with a short explanation that does not contain code-like syntax. For clarity and to retain design intent, we can change it to:

    const su2double Coeff = 1.1; // Fixed coefficient; see documentation for CFL strategy.

This preserves existing functionality while eliminating the commented-out code pattern that CodeQL flags.