Function to detect if a button/movement button is being held

1. Describe your reason for requesting this feature. What problems are you running into?
I was trying to get a custom animation system working where the character's animation loops when walking and stops after standing still. This seemed simple enough but it was quite difficult to pull off because there isn't a built in way to do something as long as a movement button is held down without futzing for a while with the event.dx and event.dy functions.

2. How would this request improve your experience with using Pulp?
This would not only help with my feature, but many other use cases, as I've seen others in the community discord run into the issue of not being able to detect a held button.