Predicted pose updates eat JustChanged events

[maluoi]

Description

StereoKit queries input poses twice per frame, once at the start of the frame, and once right before rendering to get the predicted position of poses. This can help with reducing perceived latency for input devices by a good number of milliseconds.

Unfortunately, some input checks use the button_state_ enum, which tracks change over time, and this two-query implementation can eat "just changed" events if the new value happens on the first query.

Platform / Environment

Specific to OpenXR, not always consistent due to timing.