include pressure in x-momentum flux in 1-d Cartesian

[zingale]

PR summary

previously, we were explicitly adding the pressure gradient in the conservative update
to the momentum for all 1-d geometries. But we were only doing the flux correction
on P_radial for non-Cartesian geometries. Now we treat all Cartesian geometries the
same, regardless of dimensionality.

This will likely change 1-d Cartesian answers.

PR motivation

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]

tests: http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-05-26-001/index.html

I need to understand what's happening with the SDC. I am probably double-counting there.

[zingale]

updated tests:
http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-05-28-001/index.html

[zingale]

it looks like the 1-d true SDC tests are now roundoff, although I am not sure why we'd even get that change.

[maxpkatz]

Do you know what is up with rad2Tshock-1D in that test suite run?

[zingale]

the grids are different, so fcompare aborted.

[zingale]

Here's the true-SDC (2nd order) Sod problem

[zingale]

and here's the 4th order true-SDC Sod problem

[zingale]

Here's the PPM Sod problem with 2 levels of refinement, again using this PR

[zingale]

Here's a 2D sph_in_cylcoords Sedov with 4 levels

[zingale]

closes #2467

[zingale]

tests: http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2023-10-05-002/index.html

most are reasonable, but with Detonation, all bets are off (as always).