Move reference values unit validation to utils

[marjanalbooyeh]

This PR moves a bunch of duplicated codes that validates reference units to the utils module.
Unit tests have been added for all new functionalities.

[chrisjonesBSU]

Thanks for doing this!

It looks like there might be a typo in one of the unit tests:

     def test_ref_energy_invalid_dimension_string(self, polyethylene):
        polyethylene = polyethylene(lengths=5, num_mols=1)
        system = Pack(
            molecules=[polyethylene],
            force_field=[OPLS_AA()],
            density=1.0,
            r_cut=2.5,
            auto_scale=False,
        )
        with pytest.raises(ReferenceUnitError):
>           system.reference_length = "1.0 m"
E           Failed: DID NOT RAISE <class 'hoomd_organics.utils.exceptions.ReferenceUnitError'>

Looks like system.reference_length is supposed to be system.reference_energy ?

[chrisjonesBSU]

LGTM once that last unit test passes :) Thanks!

[codecov]

Codecov Report

Merging #36 (1cd1300) into main (4b46d69) will increase coverage by 0.18%.
Report is 19 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   92.04%   92.23%   +0.18%     
==========================================
  Files          18       18              
  Lines        1320     1326       +6     
==========================================
+ Hits         1215     1223       +8     
+ Misses        105      103       -2     

Files Changed	Coverage Δ
hoomd_organics/base/system.py	88.66% <100.00%> (-1.12%)	⬇️
hoomd_organics/utils/__init__.py	100.00% <100.00%> (ø)
hoomd_organics/utils/utils.py	100.00% <100.00%> (+20.00%)	⬆️