Replace use of opaque indexes in usage of json AST - ie, `node["c"][0][2]`

[pmolodo]

As pointed out by @OleksiyPuzikov here, the use of code like this:

        def _get_path(img_c: list) -> str:
            return img_c[2][0]

...is hard to read / understand. Replace use of raw dicts/lists/tuples with named tuples or dataclasses, to make things more legible.