Use Assert.Throws for reviewed NUnit2 ExpectedException tests

Standalone opt-in port of bound NUnit2 Test/ExpectedException(typeof(E)) with an optional single non-null string literal ExpectedMessage for genuine platform ArgumentException/ArgumentNullException on closed synchronous parameterless void block methods. Preserve the original body inside a TestDelegate; enforce a supplied exact message with the bound Assert.AreEqual(object, object) overload. Requires reviewed genuine NUnit 2.5+ metadata, no implicit fixture exception handler, no NUnit result-control or NUnitException wrapper exceptions, and one runtime type identity per expected full name. Does not migrate packages, projects or other attributes and is not composed into upgrades. Skips conditional files, source API shadows, unsupported lambda effects and comments on removed attributes.