Add type annotations (parameter types and `-> None` return types) to all
top-level test functions across 22 test files. This enables mypy to
check test function bodies, catching type errors that were previously
hidden.
* Transport tests under tests/transports/
* Protocol tests under tests/protocols/
* IOT tests under iot/
* Plus some minor cleanups, most code changes are related to splitting
up smart & iot tests
