Three tests for the loadPixmap() DPI fix:
- pixmapFromSvg(content, size) renders at the exact requested size
- getMaximumDPR() returns >= 1.0
- pixmap() loaded from an SVG file has correct devicePixelRatio and
physical size matching 64 * DPR
loadPixmap() rendered all SVGs at a hardcoded 64x64 pixels regardless of
display DPI. On HiDPI screens, Qt then downscaled these low-resolution
pixmaps to the toolbar icon size, producing chunky/aliased icons.
Multiply the render size by getMaximumDPR() and tag the resulting pixmap
with the correct devicePixelRatio, matching the pattern already used in
pixmapFromSvg(const char* name, QSizeF size). This ensures SVGs are
rasterized at the physical resolution needed for crisp display.
