feat(extensions): support homogeneous tuple arguments

[wackywendell]

Description

Small PR on top of #208 that adds a .get_named_tuple::<T> method to ArgsAccess (previously ArgsExtractor), which will handle the lookup and conversions to return a Vec<T> (or error).

let scope_names = args
    .get_named_tuple::<String>("scope_names")?
    .unwrap_or_default();