Add persistent player stats and DB support

Introduce MySQL persistence and an in-memory stats system with async saving.

- Add HikariCP & MySQL connector dependencies and relocate libs in build.gradle.kts.
- Add DatabaseManager (HikariCP) to manage connection pool and lifecycle.
- Add PlayerStats data model and PlayerStatsRepository for table creation, reads, upserts and batch upserts (with prepared statements).
- Add StatsManager: coroutine-based cache, dirty-flags, async batch saves, auto-save (every 5 minutes), load/save APIs and shutdown save.
- Add StatsListener: load on AsyncPlayerPreLoginEvent and save on PlayerQuitEvent.
- Wire DB and stats into main plugin: connect on enable (disable plugin on fail), initialize StatsManager, save/disconnect on disable, register leaderboard command and stats listener.
- Update GameManager to record kills/wins/deaths and adjust scrimScore on events.
- Add LeaderboardCommand and language entries for leaderboard output; expose command in plugin.yml.
- Add database configuration section to config.yml.
- Minor refactor: KitCommand plugin accessor changed to a getter.

These changes provide a robust, pooled DB connection and efficient stats persistence (batched/upserted) to reduce DB load and ensure data safety during shutdown.

src/main/resources/languages/en_US.yml

@@ -53,6 +53,11 @@ commands:
     gameHasStarted: '<red>The game has already started. You cannot select a kit right now!</red>'
     cannotPickSameKit: '<red>You cannot pick the same kit!</red>'
     selected: '<green>You have selected <kit> as your Kit with playstyle <playstyle>!</green>'
+  leaderboard:
+    header: '<gray>====== <gold>Leaderboard</gold> ======</gray>'
+    empty: '<red>There are currently no stats</red>'
+    line: '#<rank> - <green><name></green> - <aqua><score></aqua>'
+    footer: '<gray>====== <gold>Leaderboard</gold> ======</gray>'
 
 scoreboard:
   title: '<gradient:red:gold><bold>SpeedHG</bold></gradient>'