Static Property "List" always returns all derived SmartEnum of root class

Hello,
First Thanks for your work. Just a little issue with SmartEnum "inheritance".
If you add this test in SmartEnumList.cs, it won't pass :
```
[Fact]
public void ReturnsOnlyDerivedSmartEnums()
{
var result = DerivedTestEnumWithValues1.List;

result.Should().BeEquivalentTo(DerivedTestEnumWithValues1.A, DerivedTestEnumWithValues1.B);
}
```

Start with SmartEnumList.cs and add or run the ReturnsOnlyDerivedSmartEnums test shown in the issue. Trace how DerivedTestEnumWithValues1.List gathers values, then verify that the list contains only DerivedTestEnumWithValues1.A and DerivedTestEnumWithValues1.B.

Written by the indexing model from the issue text.