Move Extensions to Core namespace

X10D.Tests/src/Core/ArrayTests.cs

@@ -1,4 +1,5 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Core;
 
 namespace X10D.Tests.Core;
 

X10D.Tests/src/Core/EnumerableTests.cs

@@ -1,5 +1,6 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using X10D.Collections;
+using X10D.Core;
 
 namespace X10D.Tests.Core;
 

X10D/src/Core/Extensions.cs

@@ -1,4 +1,4 @@
-namespace X10D;
+namespace X10D.Core;
 
 /// <summary>
 ///     Extension methods which apply to all types.