Test gg

[ilfreddy]

Tests for gaunt and gauge energy.

[ilfreddy]

@robertodr @stigrj
I have an issue here. I can run both test files separately (test_remrchem.pyand test_gaunt_gauge.py) and they both run flawlessly. If I attempt to run both the test suite crashes with the following message:
"tests/test_gaunt_gauge.py Error: /Users/runner/miniforge3/conda-bld/mrcpp_1650793508425/work/src/treebuilders/grid.cpp: copy_grid(), line 222: Incompatible MRA"

I suspect this is connected to the fact that the two files use two different MRAs. But I thought they would be independent of each other...

[ilfreddy]

Indeed if I use the same MRA in both (I had to cranck up precision for the gaunt/gaug stuff) the tests run (they fail because changing MRAs changes the result above threshold, but that's OK).