Convert compute_lamborder to C++

[maxpkatz]

PR summary

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]

radiation tests pass: http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-09-24-002/index.html

[maxpkatz]

The latest version of this PR fixes the code to make sense in all dimensions. It does this by using temporary filter arrays for the x and y dimensions in 2D and 3D respectively. It also significantly condenses the code by writing a generalized filter function (and accompanying function to load the "stencil" for both lambda and Er). This should reduce the likelihood of mistakes in the code. The boundary step at the end is also simplified into a simple loop over the entire box that copies zones from the edges and corners into the corresponding locations outside the valid region.

[zingale]

all tests pass:
http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-10-07-003/index.html