Cannot work with Pandas >= 2.0

[Ultraxime]

Hello,

Following the depreciation and then disappearance of iteritems() in aid of items(), this doesn't work with pandas >= 2.0.
As shown by the following output when using pandas 1.5.3 :

/opt/venv/lib/python3.11/site-packages/fastplot/__init__.py:183: FutureWarning: iteritems is deprecated and will be removed in a future version. Use .items instead.
  for i, l in data[c].iteritems():