TYPING: type hints for core.indexing
cc @WillAyd 

Any is added in a separate commit in case we can't come to an agreement ;)
i wonder if there is a decorator that we could use in tests to turn on reveal_type and show a summary Can you merge master? Just pushed in change to remove ABCs from _typing so should run CI again to double check sure I am with @WillAyd here about the type ignore's. I am afraid that we are never going to revisit these; we did this for a while with flake8 and it was a disaster; so I would either: actually define the type or type somewhat less until this can be fixed. > I am with @WillAyd here about the type ignore's. I am afraid that we are never going to revisit these; we did this for a while with flake8 and it was a disaster; so I would either: actually define the type or type somewhat less until this can be fixed.

fair enough. but this defeats the purpose of why I was adding type hints... to make the types of the function parameters and return types known to other functions.