Modernize hosting service test class.
Review Request #14592 — Created Sept. 4, 2025 and updated — Latest diff uploaded
The hosting service specific testcase class provides some neat
utilities, but very little of it had any type hints. This change fleshes
those out, and fixes up a couple issues with some types in the base
hosting service that this exposed. Subclasses of this have been updated
for the new generic.
Ran unit tests.