Implement deterministic simulation spine

tests/SideScrollerGame.Sim.Tests/DeterministicMathSmokeTests.cs

@@ -0,0 +1,16 @@
+using SideScrollerGame.Sim.Math;
+
+namespace SideScrollerGame.Sim.Tests;
+
+public sealed class DeterministicMathSmokeTests
+{
+    [Fact]
+    public void FixPointAverage_UsesSimulationMathTypes()
+    {
+        FixPoint16[] values = [new(1), new(2), new(3)];
+
+        var average = values.Average();
+
+        Assert.Equal(new(2), average);
+    }
+}