`Screen.dpi` tries to refer to 45° angle

[Enyium]

Running this in the Talon REPL shows that .dpi is the hypotenuse of .dpi_x and .dpi_y:

from talon import screen
import math
s = screen.containing(0, 0)
s.dpi_x
s.dpi_y
s.dpi
h = math.sqrt(s.dpi_x ** 2 + s.dpi_y ** 2); h
abs(h - s.dpi) < 0.000001
(h - s.dpi) == 0

Although even this is incorrect, because the DPI of the 45° angle would be smaller, not greater than the x or y DPI.

This is misleading, because .dpi is perceived as a tolerable substitute of .dpi_x/.dpi_y. It would be more sensible to have the average of .dpi_x and .dpi_y in .dpi.