switch to qtpy - qt-api "agnostic" qt-python-bindings

[k-dominik]

In order to prepare enabling/switching to Pyside6 (qt6!) I propose to go via qtpy. This enables us to switch qt apis more flexibly. I already tested volumina with Pyside6. With this PR, this does not require any code changes (tested python 3.13 with pyside6). Note that the qt bindings with this pr are still PyQt5.

Summary:

• change all PyQt5 import to qtpy
• change use of qApp to QApplication.instance() (doesn't exist in pyside)
• PyQt5.QtCore.pyqtSignal -> qtpy.QtCore.Signal
• PyQt5.QtCore.pyqtSlot -> qtpy.QtCore.Slot
• sip.isdeleted -> not qtpy.compat.isalive
• small gymnastics for QUndoStack which is not agnostic to the in
  binding qtpy: (PyQt5, PySide2): QtWidgets; (PyQt6, PySide6): QtGui
• Our QABC wouldn't fly anymore, I found a drop in replacement on stackoverflow.
• Added qtpy to dependencies.
• Updated min python (3.9), and the python used in conda build for tests (3.11)

Note: Should definitely be squash and merge for revertability.

[codecov]

Codecov Report

❌ Patch coverage is 61.82336% with 134 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.33%. Comparing base (eb00227) to head (3cbeba5).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
volumina/sliceSelectorHud.py	0.00%	15 Missing ⚠️
volumina/view3d/overview3d.py	0.00%	12 Missing ⚠️
volumina/quadsplitter.py	0.00%	6 Missing ⚠️
.../widgets/multiformatSlotExportFileOptionsWidget.py	0.00%	6 Missing ⚠️
volumina/view3d/meshgenerator.py	0.00%	5 Missing ⚠️
...ina/widgets/hierarchicalFileExportOptionsWidget.py	0.00%	5 Missing ⚠️
volumina/widgets/stackExportFileOptionsWidget.py	0.00%	5 Missing ⚠️
volumina/skeletons/skeletons.py	0.00%	4 Missing ⚠️
volumina/utility/shortcutManager.py	42.85%	4 Missing ⚠️
volumina/utility/shortcutManagerDlg.py	20.00%	4 Missing ⚠️
... and 35 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #333      +/-   ##
==========================================
+ Coverage   36.30%   36.33%   +0.02%     
==========================================
  Files         108      108              
  Lines       11424    11434      +10     
==========================================
+ Hits         4147     4154       +7     
- Misses       7277     7280       +3     

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[btbest]

Tried this together with the ilastik PR and seems ok I guess? Are you still planning changes?

[k-dominik]

really don't understand why the tests in the conda recipe time out...

Update: Seems to be a problem with cleaning up threads in the tests - I could not get to the root cause (I assume some changes in python) that would result in hangs when one of the tests was trying to .join some threads.

Added a fixture, where the threadpool is used implicitly and cleaned up after every test.

[btbest]

Tests green locally and sample projects load ok 👍 (ran with ilastik/ilastik#3068)