Add support for non-square pixels

[Kezii]

Add support for non-square pixels, using fractional numbers

for example, the display I'm working rn has a 2:3 pixel aspect ratio, this makes the simulator realistic to the device

[rfuest]

Thanks for the PR. This is a useful addition, but I would like to change the way it is implemented.

If this setting is named pixel aspect ratio I would expect pixel_aspect_ratio(2, 1) and pixel_aspect_ratio(4, 2) to behave the same. An alternative would be to add a pub fn scale_non_square(mut self, scale: Size) -> Self method to the output settings builder and change the type of OutputSettings::scale to Size. This should have the same functionality without having two interacting settings that determine the output pixel size.