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.

build.gradle.kts

@@ -23,8 +23,11 @@ repositories {
 dependencies {
 	implementation("fr.mrmicky:fastboard:2.1.3")
 
-	compileOnly("io.papermc.paper:paper-api:1.21.1-R0.1-SNAPSHOT")
+	implementation("com.zaxxer:HikariCP:5.1.0")
+	implementation("com.mysql:mysql-connector-j:8.4.0")
+	implementation(libs.kotlinxCoroutines)
 
+	compileOnly("io.papermc.paper:paper-api:1.21.1-R0.1-SNAPSHOT")
 	compileOnly("com.sk89q.worldedit:worldedit-core:7.2.17-SNAPSHOT")
 	compileOnly("com.sk89q.worldedit:worldedit-bukkit:7.2.17-SNAPSHOT")
 }
@@ -42,6 +45,8 @@ tasks {
 		archiveBaseName.set("GameModes-SpeedHG")
 		archiveClassifier.set("")
 		archiveVersion.set(project.version.toString())
+		relocate("com.zaxxer.hikari",  "club.mcscrims.speedhg.libs.hikari")
+		relocate("com.mysql",          "club.mcscrims.speedhg.libs.mysql")
 	}
 
 	build {