Update mypy and strengthen typing for exc hooks

[sirosen]

In order to have stronger and clearer type checking enforcement on the
exception hook registry, it has been refactored. Instead of all hooks
being declared in terms of an exception class and/or a condition
function, the hook registry stores all hooks with relevant condition
functions. Exception classes are represented (internally) by building
condition functions as necessary.

Therefore, the hook registry is now an ordered list of the form:

[(condition, hook)]

which is evaluated via a core loop:

for condition, hook in registry:
    if condition(error):
        return hook

This is effectively what the logic was before, but it is now declared
and stated as such, in a more readable manner.

One of the improved inferences was achieved by declaring a separate
interface method for registering an SDK-error-class hook. This
indicates to mypy that any condition function will be passed an SDK
error class, which allows mypy to know what attributes will
(minimally) be present.

---

A prereq for some of these changes to work was a mypy update (to v1.7.1).
This resulted in one minor, unrelated change.