adding pyqt6 and switching to qtpy

[codecov[bot]]

Codecov Report

Merging #1014 (ab17d06) into main (e1f99be) will not change coverage. The diff coverage is n/a.

:exclamation: Current head ab17d06 differs from pull request most recent head 8304f59. Consider uploading reports for the commit 8304f59 to get more accurate results

@@           Coverage Diff           @@
##             main    #1014   +/-   ##
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  Coverage   58.52%   58.52%           
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  Files          40       40           
  Lines        4567     4567           
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  Hits         2673     2673           
  Misses       1894     1894           

[landoskape]

I think this merge led to a bug that is discussed in issue #1028 and resolved in pull request #1029.