fix: add __name__ attributes to PlotLineObj for Sphinx compatibility

Author: yunjinqi

backtrader/lineiterator.py

@@ -582,6 +582,10 @@ class PlotLineObj:
                 have explicit configuration.
                 """
 
+                __name__ = 'PlotLineObj'
+                __qualname__ = 'PlotLinesObj.PlotLineObj'
+                __module__ = 'backtrader.lineiterator'
+
                 def _get(self, key, default=None):
                     """Get plotline attribute value.
 

backtrader/lineseries.py

@@ -1177,6 +1177,10 @@ class PlotLineObj:
                 have explicit configuration.
                 """
 
+                __name__ = 'PlotLineObj'
+                __qualname__ = 'PlotLinesObj.PlotLineObj'
+                __module__ = 'backtrader.lineseries'
+
                 def _get(self, key, default=None):
                     """Get plotline attribute value.