Improve thread safety and performance in core systems

Refactors event, entity, and physics management to use thread-safe and lock-free data structures (Immutable collections, ConcurrentQueue, ConcurrentDictionary, Channel) for improved concurrency and performance. Replaces O(n) queue lookups with O(1) set/dictionary checks, ensures atomic updates for shared state, and optimizes queue draining and deferred action processing. Updates related code to use new APIs and patterns, and adds documentation for thread safety and workflow.

Barotrauma/BarotraumaShared/SharedSource/Events/EventActions/UnlockPathAction.cs

@@ -1,7 +1,8 @@
 using Barotrauma.Networking;
 using Microsoft.Xna.Framework;
 using System;
-using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Threading;
 
 namespace Barotrauma
 {
@@ -10,11 +11,22 @@ namespace Barotrauma
     /// </summary>
     class UnlockPathAction : EventAction
     {
-        private static readonly HashSet<LocationConnection> pathsUnlockedThisRound = new HashSet<LocationConnection>();
+        private static volatile ImmutableHashSet<LocationConnection> _pathsUnlockedThisRound = 
+            ImmutableHashSet<LocationConnection>.Empty;
 
         public static void ResetPathsUnlockedThisRound()
         {
-            pathsUnlockedThisRound.Clear();
+            _pathsUnlockedThisRound = ImmutableHashSet<LocationConnection>.Empty;
+        }
+
+        private static void AddUnlockedPath(LocationConnection connection)
+        {
+            ImmutableHashSet<LocationConnection> original, updated;
+            do
+            {
+                original = _pathsUnlockedThisRound;
+                updated = original.Add(connection);
+            } while (Interlocked.CompareExchange(ref _pathsUnlockedThisRound, updated, original) != original);
         }
 
         public UnlockPathAction(ScriptedEvent parentEvent, ContentXElement element) : base(parentEvent, element) { }
@@ -40,7 +52,7 @@ namespace Barotrauma
                 {
                     if (!connection.Locked) { continue; }
                     connection.Locked = false;
-                    pathsUnlockedThisRound.Add(connection);
+                    AddUnlockedPath(connection);
 #if SERVER
                     NotifyUnlock(connection);
 #else
@@ -61,7 +73,7 @@ namespace Barotrauma
 #if SERVER
         public static void NotifyPathsUnlockedThisRound(Client client)
         {
-            foreach (LocationConnection connection in pathsUnlockedThisRound)
+            foreach (LocationConnection connection in _pathsUnlockedThisRound)
             {
                 NotifyUnlock(connection, client);
             }
@@ -85,4 +97,4 @@ namespace Barotrauma
         }
 #endif
     }
-}
+}