feat(cache): enable cache expiration with TTL support

- UserInfoCache now supports configurable TTL (default 24h)
- get(UUID) returns null and removes expired entries automatically
- cleanup() method is now enabled for batch cleanup
- Added scheduled cleanup task in MinerooCore (every 10 minutes)
- Added size(), clear(), and getIfPresent() helper methods

This fixes potential memory leaks from never-expiring cache entries.

paper/src/main/java/online/mineroo/paper/MinerooCore.java

@@ -77,6 +77,14 @@ public class MinerooCore extends JavaPlugin implements Listener {
       long period = 20L * 90;
       scheduler.runTaskTimer(this, new ReportPlayersTask(this, scheduler), 20L * 30, period);
     }
+
+    // Schedule cache cleanup task (every 10 minutes)
+    getServer().getScheduler().runTaskTimerAsynchronously(this, () -> {
+      if (this.userInfoCache != null) {
+        this.userInfoCache.cleanup();
+        getLogger().fine("UserInfoCache cleanup completed, size: " + this.userInfoCache.size());
+      }
+    }, 20L * 60 * 10, 20L * 60 * 10); // 10 minutes
   }
 
   @Override