Fix Discord Link RoleSyncManager thread leak

Two issues causing unbounded thread growth:

1. The repeating sync task was never cancelled on plugin disable,
   leaking the timer itself.

2. Each sync() call spawns an async task that calls
   acquireUninterruptibly() on a 5-permit semaphore. The timer fires
   up to 50 sync calls per cycle, so 45 threads block indefinitely
   waiting for permits. Before they drain, the next cycle spawns 50
   more. Threads accumulate until OOM.

Fix: cancel the task on disable, and replace acquireUninterruptibly()
with tryAcquire(5s timeout) in both sync() and unSync() so threads
don't block indefinitely — skipped syncs retry on the next cycle.

Fixes #6381

Author: JRoy

EssentialsDiscordLink/src/main/java/net/essentialsx/discordlink/EssentialsDiscordLink.java

@@ -87,6 +87,9 @@ public void onEnable() {
 
     @Override
     public void onDisable() {
+        if (roleSyncManager != null) {
+            roleSyncManager.shutdown();
+        }
         if (accounts != null) {
             accounts.shutdown();
         }

EssentialsDiscordLink/src/main/java/net/essentialsx/discordlink/rolesync/RoleSyncManager.java

@@ -7,6 +7,7 @@
 import net.essentialsx.discordlink.EssentialsDiscordLink;
 import org.bukkit.Bukkit;
 import org.bukkit.entity.Player;
+import org.bukkit.scheduler.BukkitTask;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.Listener;
 import org.bukkit.event.player.PlayerJoinEvent;
@@ -19,6 +20,7 @@
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Semaphore;
+import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 
 import static com.earth2me.essentials.I18n.tlLiteral;
@@ -28,13 +30,14 @@ public class RoleSyncManager implements Listener {
     private final Map<String, InteractionRole> groupToRoleMap = new HashMap<>();
     private final Map<String, String> roleIdToGroupMap = new HashMap<>();
     private final Semaphore syncSemaphore = new Semaphore(5);
+    private BukkitTask syncTask;
     private int syncCursor = 0;
 
     public RoleSyncManager(final EssentialsDiscordLink ess) {
         this.ess = ess;
         Bukkit.getPluginManager().registerEvents(this, ess);
         onReload();
-        this.ess.getEss().runTaskTimerAsynchronously(() -> {
+        this.syncTask = this.ess.getEss().runTaskTimerAsynchronously(() -> {
             if (groupToRoleMap.isEmpty() && roleIdToGroupMap.isEmpty()) {
                 return;
             }
@@ -67,6 +70,12 @@ public RoleSyncManager(final EssentialsDiscordLink ess) {
         }, 0, ess.getSettings().getRoleSyncResyncDelay() * 1200L);
     }
 
+    public void shutdown() {
+        if (syncTask != null) {
+            syncTask.cancel();
+        }
+    }
+
     public void sync(final UUID uuid, final String discordId) {
         final Map<String, InteractionRole> groupToRoleMapCopy = new HashMap<>(groupToRoleMap);
         final Map<String, String> roleIdToGroupMapCopy = new HashMap<>(roleIdToGroupMap);
@@ -81,7 +90,13 @@ public void sync(final Player player, final String discordId, final Map<String,
         final List<String> groups = primaryOnly ?
                 Collections.singletonList(ess.getEss().getPermissionsHandler().getGroup(player)) : ess.getEss().getPermissionsHandler().getGroups(player);
         ess.getEss().runTaskAsynchronously(() -> {
-            syncSemaphore.acquireUninterruptibly();
+            try {
+                if (!syncSemaphore.tryAcquire(5, TimeUnit.SECONDS)) {
+                    return;
+                }
+            } catch (final InterruptedException e) {
+                return;
+            }
             ess.getApi().getMemberById(discordId).thenCompose(member -> {
                 if (member == null) {
                     if (ess.getSettings().isUnlinkOnLeave()) {
@@ -151,9 +166,14 @@ public void unSync(final UUID uuid, final String discordId) {
         }
 
         ess.getEss().runTaskAsynchronously(() -> {
-            syncSemaphore.acquireUninterruptibly();
+            try {
+                if (!syncSemaphore.tryAcquire(5, TimeUnit.SECONDS)) {
+                    return;
+                }
+            } catch (final InterruptedException e) {
+                return;
+            }
             ess.getApi().getMemberById(discordId).thenCompose(member -> {
-                // Check if the member is no longer in the guild (null), they don't have any roles anyway.
                 if (member == null) {
                     return CompletableFuture.completedFuture(null);
                 }