Server: limit how far a mod may resize part of a skater for other players

- bone_scale_limit in ReSkateServer.json, and the bone-scale command:
  the most a bone may be scaled in the poses the server passes on, 1 to
  8, and its inverse the least. 1 shows every skater at the game's own
  proportions; 0 (the default, "bone-scale off") is no limit
- A "big head" mod sets one joint's scale in the body's bind pose
  (animation/dingo/cas_rsp_body_bind, the head from 1 to 4). The game
  applies it to the bone, and the bone's scale travels in every pose,
  which is how players without the mod see it. The game's own skeleton
  has no scaled joint, so 1 changes nothing for anyone else
- The player with the mod still sees it on their own screen: the server
  decides only what the others are sent
- Changing it sends whole states again, so nobody keeps a reference
  with the old sizes in it
- Dedicated servers only; a lobby's host has no such setting

Server/server_config.cpp

@@ -25,6 +25,7 @@ Json to_json(const ServerConfig &c) {
     root["max_players"] = c.max_players;
     root["reserved_slots"] = c.reserved_slots;
     root["crowd_budget"] = c.crowd_budget;
+    root["bone_scale_limit"] = c.bone_scale_limit;
     root["send_rate"] = c.send_rate;
     auto reserved = Json::array();
     for (const auto id : c.reserved) reserved.push_back(std::to_string(id)); // as strings, like the admins
@@ -132,6 +133,7 @@ ServerConfig load_config(const std::filesystem::path &file, std::vector<std::str
     c.max_players = root.value("max_players", c.max_players);
     c.reserved_slots = root.value("reserved_slots", c.reserved_slots);
     c.crowd_budget = root.value("crowd_budget", c.crowd_budget);
+    c.bone_scale_limit = root.value("bone_scale_limit", c.bone_scale_limit);
     c.send_rate = root.value("send_rate", c.send_rate);
     if (root.contains("reserved") && root.at("reserved").is_array())
         for (const auto &id : root.at("reserved")) c.reserved.push_back(steam_id(id));
@@ -258,6 +260,8 @@ std::string config_error(const ServerConfig &c) {
     if (c.reserved_slots >= c.max_players) return "reserved_slots must be less than max_players, so that anyone can join at all.";
     if (c.reserved.size() > 1024) return "reserved holds at most 1024 players.";
     if (c.send_rate < 128 || c.send_rate > 16384) return "send_rate must be 128 to 16384 (KB/s for each player).";
+    if (c.bone_scale_limit != 0 && !(c.bone_scale_limit >= 1.f && c.bone_scale_limit <= 8.f))
+        return "bone_scale_limit must be 0 (no limit) or 1 to 8 (1: no resized body parts at all).";
     if (!valid_crowd_budget(c.crowd_budget))
         return "crowd_budget must be 0 (no limit) or " + std::to_string(min_crowd_budget) + " to " +
                std::to_string(max_crowd_budget) + ".";