refactor: Deprecate array formats and default to dataframe

[eddiebergman]

trafficstars

WIP

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.84291% with 50 lines in your changes missing coverage. Please review.

Project coverage is 84.18%. Comparing base (00d1766) to head (22b6b52). Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
openml/study/functions.py	17.39%	19 Missing :warning:
openml/datasets/dataset.py	78.94%	8 Missing :warning:
openml/evaluations/functions.py	81.08%	7 Missing :warning:
openml/runs/functions.py	78.12%	7 Missing :warning:
openml/utils.py	80.00%	3 Missing :warning:
openml/extensions/sklearn/extension.py	77.77%	2 Missing :warning:
openml/setups/functions.py	94.28%	2 Missing :warning:
openml/datasets/functions.py	95.23%	1 Missing :warning:
openml/tasks/functions.py	95.00%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1372      +/-   ##
===========================================
- Coverage    84.33%   84.18%   -0.16%     
===========================================
  Files           38       38              
  Lines         5325     5230      -95     
===========================================
- Hits          4491     4403      -88     
+ Misses         834      827       -7     

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[SubhadityaMukherjee]

I am not confident in trying to merge it to develop until the tests are up and running again.