Fix Groupby Aggregation on Single Column, Single Profile DataFrame

[michaelmckinsey1]

Currently, trying to thicket.groupby("column").agg() on a single profile will error of the form

AttributeError: 'numpy.int64' object has no attribute 'to_dict'

since there is a pandas.squeeze function that returns a different type based on the shape of the dataframe. This change accounts for the case when df.shape = (1,1)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.85%. Comparing base (89ab916) to head (92e6606).

Files with missing lines	Patch %	Lines
thicket/groupby.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #253      +/-   ##
===========================================
+ Coverage    82.75%   82.85%   +0.10%     
===========================================
  Files           65       65              
  Lines         4482     4485       +3     
===========================================
+ Hits          3709     3716       +7     
+ Misses         773      769       -4     

Files with missing lines	Coverage Δ
thicket/groupby.py	91.66% <60.00%> (-0.89%)	⬇️

... and 3 files with indirect coverage changes

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