Add inner for NbtLists

[AronParker]

[Cassy343]

Thanks for taking the time to put up this contribution!

One minor nit: &Vec<T> is generally something you never see explicitly stated in Rust code, and this is because it creates a double indirection (one from the reference, and one from the Vec), and instead almost all of the time people opt for &[T] instead. Since every associated function accepting &self on Vec also exists for [T], I think it would be best to return &[NbtTag] here to avoid the anti-pattern.

That being said, NbtList already derefs to [NbtTag], so any method you'd want to call on an immutable Vec<NbtTag> can just be called directly on an NbtList (for instance my_nbt_list.chunks(2) is currently valid). I can understand adding this .inner() for consistency, but it shouldn't be blocking any use case, if that was the motivation for this PR.