Recognized Func<T> return values

As part of https://github.com/nunit/nunit/issues/4824 the `ActualValueDelegate<>` will be replaced with the standard `Func<>`

This requires `AssertHelper.UnwrapActualType` to recognize `Func<T>`  to determine the actual return type to test for compatible.

This affects NUnit2021 (EqualTo), NUnit2022, NUnit 2024, NUnit2041.
