Pathfinding / navigation mesh issues and improvements

[bm01]

Issues:

• Generated meshes are ~16 units below terrain (link).
• Pets always spawn in front of the player, causing them to clip into walls and break pathfinding.
• NPCs without a path to the player revert to default behavior, sometimes walking through objects (e.g., player jumps from a wall).
  Edit: NPCs will now stops. Pets can follow their owner by jumping to the mesh below them. On partial paths, non-pet NPCs can jump to the last node of a reverse-path (from destination to NPC).
• Recalculating a path (when the target being followed moves or when a pet receives a new order) may cause NPCs to leave the mesh due to coordinates rounding (DoL uses integers).
  Edit: Probably wasn't the cause of the issue, but fixed anyway, raycasts are performed to avoid corner cutting.
• Pathfinding is disabled when NPCs are very close to their target, often allowing them to walk through objects or leaving the mesh.
  Edit: Pathfinding is no longer disabled. Movement is finalized using raycasts.
• Door detection blocks NPC movement entirely if a door is on the path, even when alternate routes exist. Harmless in OF keeps, but problematic in NF keeps with breakable walls.
  Edit: Partially fixed, they're allowed to look for one alternative path now.
• Door detection sometimes falsely triggers if a path node is close to a door.
• Pathfinding fails when start and destination are in different zones. Currently no known impact.
  Won't fix.

Enhancements:

• Non-pet NPCs should be allowed to go through keep doors to prevent XP exploits.
• Add optional roof obstruction for Volley. de3897c
• Use mesh water data for swimming animations. Current logic relies on a single zone-wide constant, which fails in zones with inconsistent water height.
• Use closest polygon to fix NPC spawn points placed while flying.
• Use closest polygon to enforce correct ground-target placement, preventing turret/GTAoE exploits. LoS may still be inaccurate if the player casts before the GT is corrected.
• Use closest polygon to detect obvious position/fly hacks.
• Support dynamic mesh updates so pathfinding changes when structures are destroyed or built (e.g., allowing NPCs to pass through after a wall is destroyed). Won't be needed, there are smarter ways to do this.
• If no path is found, NPCs should stop instead of reverting to default behavior. Non-pet NPCs should become invincible after a few seconds and reset to prevent exploits.
  Need to think more about this.