feat: duels player colors + elytra sub-modes (M-level)

- Add ParkourGenerator.selectBlockData() hook (forced course material);
  BlockSelector checks it first; SingleDuelsGenerator overrides to use the
  player's color (16 concrete colors) and forces only DEFAULT block type
- Elytra sub-modes: SpeedDemonGenerator (max-speed score), MinSpeedGenerator
  (min-speed check, reset on 6 slow ticks), TimeTrialGenerator (score cap),
  CloseGenerator (FLAT rings); + SpeedDemon/MinSpeed/TimeTrial/Close modes,
  registration, locales play.elytra.*, config mode-settings.*
- Config.getDouble(path, default) + ConfigAccessor overload
- checkstyle 0/0, PMD 0, build green

src/main/resources/locales/en.yml

@@ -53,6 +53,26 @@ play:
       name: "&#00D4FF&lElytra"
       lore: "&#404040Fly through rings||&#404040on your elytra."
 
+    speeddemon:
+      material: "elytra"
+      name: "&#00D4FF&lSpeed Demon"
+      lore: "&#404040Reach the highest speed||&#404040possible on your elytra."
+
+    minspeed:
+      material: "elytra"
+      name: "&#00D4FF&lMin Speed"
+      lore: "&#404040Keep above the minimum speed||&#404040to fly as far as possible."
+
+    timetrial:
+      material: "elytra"
+      name: "&#00D4FF&lTime Trial"
+      lore: "&#404040Reach the target score||&#404040as fast as you can."
+
+    close:
+      material: "elytra"
+      name: "&#00D4FF&lClose"
+      lore: "&#404040Fly through flat rings||&#404040placed close together."
+
   spectator:
     name: "&#FFFFFFSpectator"