Refactor Permutations method in EnumerableExtensions to remove unnecessary logic and add validation for output count in tests

AdventOfCode.Extensions.Tests/EnumerableExtensionsTest.cs

@@ -4,13 +4,14 @@ namespace AdventOfCode.Extensions.Tests;
 public class EnumerableExtensionsTest
 {
     [Fact]
-    public void Combinations_12_2_equals_12_21()
+    public void Combinations_12_2_equals_12()
     {
         int[] data = [1, 2];
 
         var actual = data.Combinations(2).ToArray();
 
         Assert.Contains([1, 2], actual);
+        Assert.Equal(1, actual.Length);
     }
     
     [Fact]
@@ -23,6 +24,7 @@ public class EnumerableExtensionsTest
         Assert.Contains([1, 2], actual);
         Assert.Contains([1, 3], actual);
         Assert.Contains([2, 3], actual);
+        Assert.Equal(3, actual.Length);
     }
     
     [Fact]
@@ -33,6 +35,7 @@ public class EnumerableExtensionsTest
         var actual = data.Combinations(3).ToArray();
 
         Assert.Contains([1, 2, 3], actual);
+        Assert.Equal(1, actual.Length);
     }
     
     [Fact]
@@ -46,6 +49,7 @@ public class EnumerableExtensionsTest
         Assert.Contains([1, 2], actual);
         Assert.Contains([2, 1], actual);
         Assert.Contains([2, 2], actual);
+        Assert.Equal(4, actual.Length);
     }
     
     [Fact]
@@ -62,5 +66,6 @@ public class EnumerableExtensionsTest
         Assert.Contains([3, 1], actual);
         Assert.Contains([3, 2], actual);
         Assert.Contains([3, 3], actual);
+        Assert.Equal(9, actual.Length);
     }
 }