Fix: Restore QObject on PrivateData to fix segfault while keeping caching optimizations

	* [FIX] Restore QObject as base class for all three PrivateData classes:
 	 	- QwtText_PrivateData
 		- QwtAbstractScaleDraw_PrivateData
  		- QwtScaleDraw_PrivateData
  		→ resolves segfault during lifecycle / teardown

Author: dappham-CODRA

qwt/scale_draw.py

@@ -24,6 +24,7 @@
 
 from qtpy.QtCore import (
     QLineF,
+    QObject,
     QPoint,
     QPointF,
     QRect,
@@ -50,22 +51,11 @@
 _ALIGN_BOTTOM = int(Qt.AlignBottom)
 
 
-class QwtAbstractScaleDraw_PrivateData(object):
-    # See QwtText_PrivateData: ``QObject`` inheritance is unused and the
-    # base class' ``__init__`` is a measurable cost in tick-heavy renders.
-    __slots__ = (
-        "spacing",
-        "penWidth",
-        "minExtent",
-        "components",
-        "tick_length",
-        "tick_lighter_factor",
-        "map",
-        "scaleDiv",
-        "labelCache",
-    )
+class QwtAbstractScaleDraw_PrivateData(QObject):
+    # QObject base class restored for Qt parent/child ownership semantics.
 
     def __init__(self):
+        QObject.__init__(self)
         self.spacing = 4
         self.penWidth = 0
         self.minExtent = 0.0
@@ -492,20 +482,11 @@ def invalidateCache(self):
         self.__data.labelCache.clear()
 
 
-class QwtScaleDraw_PrivateData(object):
-    # See QwtText_PrivateData: ``QObject`` inheritance is unused and the
-    # base class' ``__init__`` is a measurable cost in tick-heavy renders.
-    __slots__ = (
-        "len",
-        "alignment",
-        "orientation",
-        "labelAlignment",
-        "labelRotation",
-        "labelAutoSize",
-        "pos",
-    )
+class QwtScaleDraw_PrivateData(QObject):
+    # QObject base class restored for Qt parent/child ownership semantics.
 
     def __init__(self):
+        QObject.__init__(self)
         self.len = 0
         self.alignment = QwtScaleDraw.BottomScale
         # Cached orientation - kept in sync by ``QwtScaleDraw.setAlignment``

qwt/text.py

@@ -557,26 +557,11 @@ def textMargins(self, font):
         return 0, 0, 0, 0
 
 
-class QwtText_PrivateData(object):
-    # ``QObject`` was previously used as the base class but no Qt signals
-    # or events are ever emitted from ``_PrivateData`` containers and the
-    # ``QObject.__init__`` call dominates ``QwtText.__init__`` (it is the
-    # single most expensive line for tick-label-heavy renders, see
-    # https://github.com/PlotPyStack/PythonQwt/issues/93).
-    __slots__ = (
-        "renderFlags",
-        "borderRadius",
-        "borderPen",
-        "backgroundBrush",
-        "paintAttributes",
-        "layoutAttributes",
-        "textEngine",
-        "text",
-        "font",
-        "color",
-    )
+class QwtText_PrivateData(QObject):
+    # QObject base class restored for Qt parent/child ownership semantics.
 
     def __init__(self):
+        QObject.__init__(self)
         self.renderFlags = Qt.AlignCenter
         self.borderRadius = 0
         self.borderPen = Qt.NoPen