Test databases in internal/handlers and internal/service were named
after the address of the running test. A later test could get the
address of a finished one, and with it a database that test's server
might still hold open. Each test database now gets a random name, as
in internal/ircserver.
A new test in each package opens two test databases at once and checks
that they do not share one; both new tests fail with the old names.
Model: opus-5-5