Implement master db and basic user store

src/Data/UserDataStore.cs

@@ -0,0 +1,24 @@
+namespace MariesWonderland.Data;
+
+public class UserDataStore
+{
+    private readonly Dictionary<long, DarkUserMemoryDatabase> _users = new();
+
+    public DarkUserMemoryDatabase GetOrCreate(long playerId)
+    {
+        if (!_users.TryGetValue(playerId, out var db))
+        {
+            db = new DarkUserMemoryDatabase();
+            _users[playerId] = db;
+        }
+        return db;
+    }
+
+    public bool TryGet(long playerId, out DarkUserMemoryDatabase db)
+        => _users.TryGetValue(playerId, out db!);
+
+    public void Set(long playerId, DarkUserMemoryDatabase db)
+        => _users[playerId] = db;
+
+    public IReadOnlyDictionary<long, DarkUserMemoryDatabase> All => _users;
+}