feat: turrents and explosions

Interfaces/ILevel.cs

@@ -4,5 +4,13 @@ namespace GodotHostTest.Interfaces;
 
 public interface ILevel
 {
+    /// <summary>
+    ///     Time between successive spawns.
+    /// </summary>
     public TimeSpan TimeBetweenSpawns { get; }
+
+    /// <summary>
+    ///     Duration of a single spawn.
+    /// </summary>
+    public TimeSpan SpawnDuration { get; }
 }