fix(display): Do LVGL task processing in main on POSIX.
An SDL/Zephyr bug prevents proper display when SDL calls are
made from anything but the main thread, so add task handling
in our simple main function when on POSIX.
fix(usb): Compilation fix for 64-bit targets
Properly handle differences in the size of `size_t` on 64-bit
architectures.
fix(display): Imply, but don't force, LVGL mono theme
Some targets may be using color displays, so instead of forcing
on the mono theme, merely imply it to default it
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