feat(physics): movement blockers the server's movers can't walk through

Enemies are moved along navmesh paths without collision, so a wall only stops
them if their path stops at it. dpWorld now keeps a list of such walls, each
with the collision filter it blocks with, and cuts a path where it first walks
into one (a little short of the wall; a mover inside one can walk out).

Which objects block comes from data (dpMovementBlockers::BlockingFilter):
- navmesh carvers (navmesh_carver in the level config, which the client reads
  with add_to_navmesh and carver_only) block every mover;
- solid objects whose collision group touches enemies and not players (group 18,
  e.g. "FV - Enemy Blocking Volume", "PR - Pet Blocker") block what that group
  touches.

dpShapeBox gains SegmentEntry, a segment test against the rotated box.

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

dPhysics/dpShapeBox.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "dpShapeBase.h"
+#include <optional>
 #include <vector>
 #include "NiPoint3.h"
 #include "NiQuaternion.h"
@@ -39,6 +40,13 @@ public:
 	 */
 	float SquaredDistanceTo(const NiPoint3& point) const;
 
+	/**
+	 * Where the segment from a to b first goes into the box, as a fraction of the way from a to b (0 to 1), tested
+	 * against the box's real (rotated) shape. Empty when the segment misses the box, or starts inside it (so
+	 * something already in the box can always leave it).
+	 */
+	std::optional<float> SegmentEntry(const NiPoint3& a, const NiPoint3& b) const;
+
 	void InitVertices();
 
 	void SetPosition(const NiPoint3& position);