ludic.zones: a disc per player from their fog, merged into clusters; the simulating packages ask whether a place is simulated

zones_set / zones_clear / zones_merge, zones_contains / zones_nearest and the clusters' bounding circles,
over fixed arrays of ZONES_MAX (16). WildlifeWorld.active freezes an animal outside (no state change, no
dice), NpcWorld.active a walker (and no birth outside), VehicleWorld.active a moored boat, and
ThingsWorld.restocks keeps a morning's restock inside; every default is "everywhere", so an unbound game
is unchanged. Tests: the merge (near players one cluster, far two, a player leaving splits a chain),
contains, nearest, the radius; wildlife, npc, vehicles and things pass as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.npc/port.ludic

@@ -5,6 +5,7 @@ export port NpcWorld {
   water: fn(float, float) -> float = fn nw_dry             # the water's surface there
   slope: fn(float, float) -> float = fn nw_zero2
   allowed: fn(float, float) -> bool = fn nw_yes2           # a person may stop here (not the player's camp)
+  active: fn(float, float) -> bool = fn nw_yes2            # simulated here: outside, a walker is frozen and none is born
   # (x, z, r, feet, head): true when a still thing takes a body of radius r there; pushed_x / _z say where
   push: fn(float, float, float, float, float) -> bool = fn nw_no_push
   pushed_x: fn() -> float = fn nw_asked_x