Proper label scoping in macro

[lightclient]

In #69 we added a random postfix to label names to create a scope. It would be nice to have better guarantees about the scope and not rely on the small possibility of label collisions.

A few ideas we had:

• Expand the capabilities of Ingest to support expanding macros. This is not trivial because the Independent scope is truly independent and needs no external data to fully assemble its ops. This is not the same assumption that instruction macros make, because they can use labels from the outer scope and when concretized they need to have an understanding of where they've been invoked in terms of concrete ops.
• Use a sub-assembler, like with the push macro. Unfortunately it likely falls victim of the same issues as above.
• Create a new Scope enum in the assembler module and expand the Label type to be a name and scope. This seems messy and it's annoying to have another Scope type.