Improve path safety

Right now, every Movement just expects that the player is standing in `src`. However when things get screwed up that isn't the case. And there are some really crappy heuristics that it uses. For example traverse jumps when its Y level is below what it expects it to be even though that's NOT its job. Instead of canceling the path if it's been more than 2 blocks away for more than 5 seconds, it should immediately cancel it when the player is off the path. This also helps if the real player is trying to take over (like if there's a mob) and doesn't want to type cancel, they can divert away from the path.