Use the original Flutter image and source hotspot with explicit DPR, retaining the existing view and minimum-size policies. Pin the plugin implementation from rustdesk-org/flutter_custom_cursor#1.
Keep Linux/macOS bitmap sizing and painted cursor DPI
conversion consistent, and derive hotspots from the actual scaled bitmap.
Pad tall Linux native cursor buffers with transparency to
preserve the lower half in the hardware cursor plane.
Cover bitmap sizing, hotspots, artwork preservation,
and painting with focused regression tests.
