For wtv reason on nixos importing `pyqtgraph` first is causing `numpy`
to fail import?? No idea, but likely something to do with recent
`flake.nix`'s ld-lib-linking with `<nixpkgs>` marlarky?
- set `QT_USE_PHYSICAL_DPI='1'` env var for Qt6 high-DPI
* we likely want to do this in `piker.ui` as well!
- move `pxr` calc from widget to per-screen in loop.
- add `unscaled_size` calc using `pxr * size`.
- switch from `.availableGeometry()` to `.geometry()` for full
bounds.
- shorten output labels, add `!r` repr formatting
- add Qt6 DPI rounding policy TODO with doc links
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Buncha updates and improvements,
- adjust sub-namespace imports according to console warnings.
- iterate all detected screens in a loop and instead report which is the
primary and the current.
- type annotate all vars where non-obvious, particularly the`Qt` refs.