Honor set_rlabel_position on partial-wedge polar axes - #32539

PR summary

Closes #15835.

PolarAxes.draw replaces the r-axis label transform with _yaxis_transform whenever the axes shows a partial wedge, and that transform drops _r_label_position entirely, so set_rlabel_position silently does nothing on wedge plots.

This adds _r_label_position_manual, set by set_rlabel_position and cleared on clear(). When the position was set manually, the labels now use the same rlabel-aware transform as on a full circle, RadialTick.update_position derives rotation and anchors from the rlabel angle, and the tick pad shifts along the rlabel ray (the existing _ThetaShift mode 'rlabel'). A manual position is honored even if it lies outside the wedge, as suggested in the issue. The default behavior is unchanged: without a manual position the labels still hug the wedge edges, so no existing plot changes. set_rgrids no longer re-calls set_rlabel_position when no angle is passed, which would otherwise mark the position as manual without moving anything.

AI Disclosure

I used AI agents to help trace the transform chain and to draft the fix and the test. I reviewed, understood and ran all of it myself before opening this PR.

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