Expand rules_python's type checking in CI to apply to remaining code

[ctcjab]

...where type errors are still prone to getting introduced.

Quoting @aignas in https://github.com/bazel-contrib/rules_python/pull/3240#issuecomment-3384929943

I personally am not against doing type checking against all of the python code within the repo, but that is a fair amount of work that would definitely benefit from community also pitching in. I'll create a place-holder ticket that is reasonably wide (and we already have a CI job that is doing type checking on the runfiles library), so initially we could use something similar in our initial approach.