Implement two new List constructors: `List.new(size)` creates a list of given size initialized to null, and `List.new(size, default)` creates a list with all elements set to the provided default value. Add corresponding C primitives `list_newWithSize` and `list_newWithSizeDefault` in wren_core.c, register them in the core initialization, and include test coverage for both constructors. Also add Max Ferguson to AUTHORS.
