Move all remaining OmniSci tests to `rbc/tests/heavyai/`

[tupui]

After moving, CI should also be changed:

- mamba run -n rbc pytest -sv -r A rbc/tests/ -x -k heavyai
+ mamba run -n rbc pytest -sv -r A rbc/tests/heavyai/ -x

[guilhermeleobas]

There are two test files (test_externals_cmath.py and test_externals_libdevice.py), which are not in rbc/tests/heavydb and uses the heavydb fixture.