Convert correct_dterm to C++

[maxpkatz]

PR summary

This uses inline metric calculation to support GPU offloading. Note that the vector s was unused and was previously only in the code to enable the call to sphe to fill in re for spherical geometries, which is now handled through edge_center_metric if we're in a spherical geometry. We also do a loop over dimensions to make the code a little more understandable.

PR checklist

• test suite needs to be run on this PR
• this PR will change answers in the test suite to more than roundoff level
• all newly-added functions have docstrings as per the coding conventions
• the CHANGES file has been updated, if appropriate
• if appropriate, this change is described in the docs

[zingale]

all tests pass:
http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-10-09-004/index.html