[Experimental] Modify prox trigger handling

Proximity triggers were handled fairly inefficiently, especially on
servers with high player / NPC counts but few proximity triggers.
It also fixes issues where proximity triggers would fail to fire if a
player stood still but the NPC moved away.
I say experimental because it redirects the logic pretty heavily, and
has only underwent my usual quick testing, while this probably needs to
be tried on a large server / against existing prox-trigger heavy
scripts.
Fix cuboid, entityScript errors

- cuboids identified wrong
- cuboids calculating what was 'within' (EG for list_players)
incorrectly (Z wasn't rounded)
- entity script helper error if entity event fires in the middle of
Denizen's init sequence somehow.