add Factions and FactionsExtensions classes

src/game-lib/Model/Factions.cs

@@ -0,0 +1,17 @@
+using System.Text.Json.Serialization;
+
+namespace UfoGameLib.Model;
+
+public class Factions : List<Faction>
+{
+    [JsonConstructor]
+    public Factions()
+    {
+    }
+
+    public Factions(IEnumerable<Faction>? factions = null)
+        => AddRange(factions ?? new List<Faction>());
+
+    public Factions DeepClone()
+        => new Factions(this.Select(faction => faction.DeepClone()));
+}

src/game-lib/Model/FactionsExtensions.cs

@@ -0,0 +1,7 @@
+namespace UfoGameLib.Model;
+
+public static class FactionsExtensions
+{
+    public static Factions ToFactions(this IEnumerable<Faction> factionsEnumerable) 
+        => new Factions(factionsEnumerable);
+}