Add some Qt DPI extras to `qt_screen_info.py`

- 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

snippets/qt_screen_info.py

@@ -31,6 +31,7 @@ Resource list for mucking with DPIs on multiple screens:
 - https://doc.qt.io/qt-5/qguiapplication.html#screenAt
 
 '''
+import os
 
 from pyqtgraph import QtGui
 from PyQt6 import (
@@ -44,6 +45,10 @@ from PyQt6.QtCore import (
     QRect,
 )
 
+
+# https://doc.qt.io/qt-6/highdpi.html#environment-variable-reference
+os.environ['QT_USE_PHYSICAL_DPI'] = '1'
+
 # Proper high DPI scaling is available in Qt >= 5.6.0. This attibute
 # must be set before creating the application
 if hasattr(Qt, 'AA_EnableHighDpiScaling'):
@@ -58,13 +63,22 @@ if hasattr(Qt, 'AA_UseHighDpiPixmaps'):
         True,
     )
 
+# NOTE, inherits `QGuiApplication`
+# https://doc.qt.io/qt-6/qapplication.html
+# https://doc.qt.io/qt-6/qguiapplication.html
 app = QtWidgets.QApplication([])
+#
+# ^TODO? various global DPI settings?
+# [ ] DPI rounding policy,
+# - https://doc.qt.io/qt-6/qt.html#HighDpiScaleFactorRoundingPolicy-enum
+# - https://doc.qt.io/qt-6/qguiapplication.html#setHighDpiScaleFactorRoundingPolicy
+
 window = QtWidgets.QMainWindow()
 main_widget = QtWidgets.QWidget()
 window.setCentralWidget(main_widget)
 window.show()
 
-pxr: float = main_widget.devicePixelRatioF()
+_main_pxr: float = main_widget.devicePixelRatioF()
 
 # explicitly get main widget and primary displays
 current_screen: QtGui.QScreen = app.screenAt(
@@ -77,7 +91,13 @@ for screen in app.screens():
     name: str = screen.name()
     model: str = screen.model().rstrip()
     size: QSize = screen.size()
-    geo: QRect = screen.availableGeometry()
+    geo: QRect = screen.geometry()
+
+    # device-pixel-ratio
+    # https://doc.qt.io/qt-6/highdpi.html
+    pxr: float = screen.devicePixelRatio()
+
+    unscaled_size: QSize = pxr * size
     phydpi: float = screen.physicalDotsPerInch()
     logdpi: float = screen.logicalDotsPerInch()
     is_primary: bool = screen is primary_screen
@@ -88,11 +108,12 @@ for screen in app.screens():
         f'|_primary: {is_primary}\n'
         f' _current: {is_current}\n'
         f' _model: {model}\n'
-        f' _screen size: {size}\n'
-        f' _screen geometry: {geo}\n'
-        f' _devicePixelRationF(): {pxr}\n'
-        f' _physical dpi: {phydpi}\n'
-        f' _logical dpi: {logdpi}\n'
+        f' _size: {size}\n'
+        f' _geometry: {geo}\n'
+        f' _devicePixelRatio(): {pxr}\n'
+        f' _unscaled-size: {unscaled_size!r}\n'
+        f' _physical-dpi: {phydpi}\n'
+        f' _logical-dpi: {logdpi}\n'
     )
 
 # app-wide font info
@@ -110,8 +131,8 @@ str_w: int = str_br.width()
 
 print(
     f'------ global font settings ------\n'
-    f'font dpi: {fontdpi}\n'
-    f'font height: {font_h}\n'
-    f'string bounding rect: {str_br}\n'
-    f'string width : {str_w}\n'
+    f'font dpi: {fontdpi!r}\n'
+    f'font height: {font_h!r}\n'
+    f'string bounding rect: {str_br!r}\n'
+    f'string width : {str_w!r}\n'
 )