Add unit test for Apply

Funcky.Test/FunctionalClass/ApplyTest.cs

@@ -0,0 +1,23 @@
+using static Funcky.Discard;
+
+namespace Funcky.Test.FunctionalClass;
+
+public class ApplyTest
+{
+    [Fact]
+    public void CanApplyParametersInAnyOrder()
+    {
+        var func = Linear0;
+        var f1 = Fn(Linear0).Apply(__, __, 10);
+        var f2 = func.Apply(2, __, 7);
+        var f3 = Apply(Fn(Linear0), 42, __, __);
+        Assert.Equal(Linear0(10, 2, 10), f1(10, 2));
+        Assert.Equal(Linear0(2, 10, 7), f2(10));
+        Assert.Equal(Linear0(42, 10, 2), f3(10, 2));
+    }
+
+    public static T Fn<T>(T value) => value;
+
+    private static int Linear0(int a, int b, int c)
+        => a + (b * c);
+}