Small ResourceManager refactor, add ResourceSaver<T>.

TestGame/TestPlayer.cs

@@ -5,6 +5,7 @@ using DaggerFramework.Utils;
 
 public class TestPlayer : RectangleShape2d
 {
+    public float SprintSpeed { get; set; } = 400f;
     protected override void OnStart()
     {
         base.OnStart();
@@ -26,7 +27,7 @@ public class TestPlayer : RectangleShape2d
         base.OnUpdate(dt);
 
         var sprinting = Input.IsActionDown("sprint");
-        _speed = sprinting ? 400f : 200f;
+        _speed = sprinting ? SprintSpeed : 200f;
 
         var velocity = Input.GetInputDirection("left", "right", "up", "down") * _speed;
         Position += velocity * (float)dt;