Autonomous players: finer stuck detection and per-goal guard

A long detour (tunnel) is no longer mistaken for being stuck, and a player who walks 3 minutes towards the same NPC without reaching it gives up for half an hour.

Long detours: a route that first moves away from its target as the crow flies, like the Coldridge Pass tunnel to Kharanos, was mistaken for being stuck. A target is now set aside only if the player also failed to move at least 8 m during the observation window.
Per-goal guard: whatever the path, 3 cumulative minutes (out of 10) walking towards the same NPC (quest turn-in or pickup, vendor, class trainer) without reaching it sets that NPC aside for 30 minutes. No more queues of players shuffling behind an obstacle.