[ENH]: Track PieContainer in Axes.containers

Problem

Following up on #30733 where adding PieContainer to ax.containers was deferred: downstream export/conversion libraries such as plotly (and pandas plotting users) cannot discover or reconstruct pie plots from an Axes instance because PieContainer is not retained anywhere on the Axes. Once ax.pie() finishes, only disconnected Wedge patches remain in ax.patches.

Proposed solution

Would you be open to an ABC/Protocol for Container that relaxes the tuple inheritance so PieContainer can be tracked in ax.containers?