Add init files to subfolders in tests to fix code coverage

[gsheni]

No description provided.

[codecov]

Codecov Report

Merging #60 into main will increase coverage by 53.38%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main      #60       +/-   ##
===========================================
+ Coverage   43.47%   96.86%   +53.38%     
===========================================
  Files           8       10        +2     
  Lines         184      319      +135     
===========================================
+ Hits           80      309      +229     
+ Misses        104       10       -94     

Impacted Files	Coverage Δ
data_tables/tests/data_table/test_datatable.py	100.00% <0.00%> (ø)
data_tables/tests/data_column/test_data_column.py	100.00% <0.00%> (ø)
data_tables/tests/conftest.py	100.00% <0.00%> (+28.57%)	⬆️
data_tables/data_table.py	92.42% <0.00%> (+68.18%)	⬆️
data_tables/data_column.py	100.00% <0.00%> (+85.45%)	⬆️

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