Consider implementing custom `__eq__` for indices classes

[pipermerriam]

NOTE: it isn't clear whether there is much benefit to be gained from this approach but worth considering for added safety.

We use custom integer subclasses for the various indices types. A naive comparison of 1 == LocalIdx(1) will currently return True.

If we want to be extra strict we should consider implementing __eq__ methods on these to differentiate them from 1) each other and 2) base int values.