AudioClassificationData docstrings

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #1096 (412db10) into master (29c182f) will increase coverage by 0.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1096      +/-   ##
==========================================
+ Coverage   87.82%   88.01%   +0.19%     
==========================================
  Files         281      281              
  Lines       12804    12807       +3     
==========================================
+ Hits        11245    11272      +27     
+ Misses       1559     1535      -24     

Flag	Coverage Δ
unittests	88.01% <100.00%> (+0.19%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/image/classification/data.py	97.54% <ø> (ø)
flash/audio/classification/data.py	100.00% <100.00%> (+21.81%)	⬆️
flash/audio/classification/input.py	96.25% <100.00%> (+15.00%)	⬆️

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