Add RankingManager and integrate RR system

Introduce a new RankingManager that implements a per-round Rank Rating (RR) system (placement + kill-based scoring, placement games, kill caps and RR interpolation). Wire the manager into the plugin (SpeedHG): add field + initialization. Integrate into GameManager: call startRound at game start, registerRoundKill on kills, and onPlayerResult for eliminated players and the winner; adjust some stats calls (addLoss/addWin kept alongside ranking updates). Add corresponding English language messages for placement progress and result notifications.

src/main/resources/languages/en_US.yml

@@ -19,6 +19,11 @@ game:
   death-pve: '<prefix><yellow><player> has died! There are <left> players left.</yellow>'
   win-chat: '<prefix><green><winner> has won the game! Thanks for playing!</green>'
 
+ranking:
+  placement_progress: '<prefix><gray>Placement <aqua><current>/<total></aqua> — Placed <aqua>#<placement></aqua> · <aqua><kills></aqua> Kill(s)</gray>'
+  result_win:  '<prefix><gold>🏆 Victory!</gold> <gray>Kills: <aqua><kills></aqua></gray> · <rr>'
+  result_loss: '<prefix><gray>You placed <aqua><placement></aqua> · Kills: <aqua><kills></aqua></gray> · <rr>'
+
 title:
   fight-main: '<red>The battle has begun!</red>'
   fight-sub: '<red>Try not to die!</red>'