Implement `walk()` and `walk_rand()`

[ike709]

• Implemented walk(). Including walk(Ref, 0) to cease any walking.
• Implemented walk_rand()
• Added a helper for getting a random dir
• Added a GetStep() overload that takes dir as an integer directly, to avoid redundant casting.
• speed is now ignored in WalkManager, rather than the native walk-related procs
• Properly flags walk_to() as unimplemented

https://github.com/user-attachments/assets/dd802c99-afa4-4720-950f-c68563211b53