feat: add Elytra mode (basic S-level)

- elytra/section/: ElytraSection (5 knots + cubic spline via commons-math3),
  ElytraKnotDirector (dx~N(75,15), dy bias, dz~N(0,35)), ElytraPointType
  (CIRCLE Bresenham / FLAT), ClientBlockChanger (client-side sendBlockChanges,
  forward-limit min(vd,8))
- elytra/generator/ElytraGenerator extends ParkourGenerator: own tick() (score by
  velocity.x while gliding, section lifecycle, fall detection, sustained boost in
  ascending sections), reset, spawn with elytra
- elytra/mode/ElytraMode: registered in Modes/PluginBootstrap, locale items ru/en
- build.gradle: commons-math3 3.6.1 + relocate
- checkstyle 0/0, PMD 0, build green (tests + shadowJar)

src/main/resources/locales/ru.yml

@@ -44,6 +44,14 @@ play:
       name: "&#FF44FF&lНевидимый барьер"
       lore: "&#404040Невидимые блоки с||&#404040цветными контурами из частиц"
 
+  elytra:
+    name: "&#FFFFFFЭлитры"
+
+    elytra:
+      material: "elytra"
+      name: "&#00D4FF&lЭлитры"
+      lore: "&#404040Летай сквозь кольца||&#404040на элитрах."
+
   spectator:
     name: "&#FFFFFFНаблюдатель"