Skip CSV output for x-y points

[nfahlgren]

Describe your changes
json2csv checks for list and tuple data types and unpacks them into a long-format CSV output file. But when the value is a list of tuples, for storing coordinates, it was outputting the comma-delimited coordinates into the CSV output, which caused the table to be parsed with an uneven number of columns.

This PR checks the type of the data contained in the enclosing list or tuple and skips it if it is also a list or tuple.

Type of update
Is this a: Bug fix

Associated issues
#1191

For the reviewer
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• PR functionality reviewed in a Jupyter Notebook
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[codecov]

Codecov Report

Merging #1198 (6139ff3) into main (ee42f4f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1198   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          141       141           
  Lines         6023      6024    +1     
=========================================
+ Hits          6023      6024    +1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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

Impacted Files	Coverage Δ
plantcv/utils/converters.py	100.00% <100.00%> (ø)