MNT: Move some calls to children classes to stop pyside6 throwing an error about __init__ in classes that use multiple inheritence.

[nstelter-slac]

There is no issue running on pyqt5, but on pyside6 throws a runtime error when initializing classes that use multiple inheritance of a qt base class and a pydm class.

example class:

    class PyDMDrawing(QWidget, PyDMWidget, new_properties=_penRuleProperties))
    ...
    def __init__(self, parent=None, init_channel=None):
       ...
       # explicitly calling base class __init__ functions
       QWidget.__init__(self, parent)
       PyDMWidget.__init__(self, init_channel=init_channel)
       ...

The runtime error happens when a call is made in the base class that relies on the qt base class's __init__ call to have completed setting things up (such as 'installEventFilter()).

example error:

    -> self.installEventFilter(self)
    RuntimeError: '__init__' method of object's base class (PyDMDrawingImage) not called

This error is thrown despite that we explicitly call each of it's base class __init__ functions. It seems like pyside6 is just being extra cautious here.

The fix here is to move these "problem" calls out of our pydm base classes __init__ and into the children class's __init__, after we explicity call the parent class constructors. To match the functionality of b4, these calls need to be added to any classes with PyDMWidget as their parent.

[nstelter-slac]

this patch addresses the same issue discussed here: #1177

[YektaY]

Have you looked to see if __init_subclass__ could work in this case? https://peps.python.org/pep-0487/

[nstelter-slac]

Have you looked to see if _init_subclass_ could work in this case? https://peps.python.org/pep-0487/

yes i messed around a bit with _init_subclass_, but it seems like it only gets called at subclass creation time (as opposed to subclass instance creation time).

meaning we get access to "cls" but not "self", so in it we could only modify class attributes like 'RULE_PROPERTIES', which are vars shared across all instances of the class