Interesting game.
Unfortunately the keyboard controls are very laggy on my computer, which initially made it impossible to play until I figured out a way to fix it temporarily by changing an operating system setting.
If I hold down walking keys for a while, and then try to stop walking, my character continues walking for a long time after I stop pressing any buttons. It seems like key repeat events must be getting added to a queue, and if I've held down keys for too long, the event queue fills up faster than the events are handled. Mouse events are apparently handled separately from keyboard events, because mouse movements and clicks are practically immediate and never laggy. I decreased the key repeat speed in my operating system settings (I like a high repeat speed for typing) and that fixed the issue.
To really fix it, you could avoid processing the key repeat events entirely, and only process key-down and key-up events. Apparently Godot calls key repeats "echo events", so you could just check if `InputEvent.is_echo()` is true. Then for key down and up, there's `InputEvent.is_action_pressed()` and `InputEvent.is_action_released()`