Use existing np.arrays when calling _qhull.delaunay - #32417

PR summary

Triangulation.__init__ converts array-like x and y arguments into numpy arrays and stores as self.x and self.y. However, it passes the original arrays to _qhull.delaunay, which converts again as part of pybind11 bridging.

Instead, pass the numpy arrays.

AI Disclosure

None used for this specific fix. Found while working on #32411 where I did use AI.

PR quality check

• Use an expressive title, e.g. "Fix title font property precedence"
• [/] New and changed code is tested
• [/] Plotting related features are demonstrated in an example
• [/] New features and API changes have release notes
• [/] Documentation complies with general and docstring guidelines