Remove unnecessary conversions to numpy arrays (fixes gsd writer issue), remove self.atomistic from __repr__ method.

[chrisjonesBSU]

I've been running into a couple issues.

1. gsd.hoomd errors out during a validation step before writing a new snapshot to file. This is caused by converting the bond_types list to an array before appending the snapshot to the new gsd file.

In gsd.hoomd

        if name == 'types':
            matches_default_value = data == container._default_value[name]

container._decult_value[name] is an empty list for bonds/angles/dihedrals, and data (passed in by grits) was an array of strings, resulting in numpy-related broadcast error.

A quick example here:

>>> myarr = np.array(["A", "B"])
>>> myarr == []
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operands could not be broadcast together with shapes (2,) (0,)
>>> mylist = ["A", "B"]
>>> mylist == []
False
>>>

2. self.atomistic is throwing an error only when calling the visualize() method. I'm fairly certain this is caused by cloning of the compound which we've added some custom attributes to. I think it's fine to remove this bit of information from the __repr__ method only, the attribute itself is still there, and works when called directly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.98%. Comparing base (9676c7b) to head (759a753).
Report is 23 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #95   +/-   ##
=======================================
  Coverage   94.98%   94.98%           
=======================================
  Files           4        4           
  Lines         459      459           
=======================================
  Hits          436      436           
  Misses         23       23           

Files with missing lines	Coverage Δ
grits/coarsegrain.py	95.94% <100.00%> (ø)

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