PR summary

PR checklist

• [ x] "closes [ENH]: Modifier key to discretize rotations for 3D plots #31093" is in the body of the PR description to link the related issue
• [x ] new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

Description

This PR adds a Ctrl modifier key to 3D mouse rotation so that when Ctrl is held while dragging, the view angles snap to fixed 5° increments (azimuth/elevation/roll). This makes it easier to return to repeatable camera angles when exploring 3D plots.

A small test is included to verify snapping behavior when Ctrl is pressed.