KiokuDB::TypeMap::Shadow - Try a list of KiokuDB::TypeMaps in order

    KiokuDB->new(
        backend => ...,
        typemap => KiokuDB::TypeMap::Shadow->new(
            typemaps => [
                $first,
                $second,
            ],
        ),
    );

This class is useful for performing mixin inheritance like merging of typemaps, by shadowing an ordered list.

This is used internally to overlay the user typemap on top of the KiokuDB::TypeMap::Default instance provided by the backend.

This differs from using includes in KiokuDB::TypeMap because that inclusion is computed symmetrically, like roles.