There was a very strange legacy test
`test_spawning.test_local_arbiter_subactor_global_state` which was
causing unforseen hangs/errors on the UDS tpt and looking deeper this
test was already doing root-actor things that should never have been
valid XD
So rework that test to properly demonstrate something of value
(i guess..) and add a new suite which start more rigorously auditing our
`open_root_actor()` permitted usage.
For the old test,
- since the main point of this test seemed to be the ability to invoke
the same function in both the parent and child actor (using the very
legacy `ActorNursery.run_in_actor()`.. due to be deprecated) rename it
to `test_run_in_actor_same_func_in_child`,
- don't re-enter `.open_root_actor()` since that's invalid usage (tested
in new suite see below),
- adjust some `spawn()` arg/var naming and ensure we only return in the
child.
For the new suite add tests for,
- ensuring the implicit `open_root_actor()` call under `open_nursery()`.
- double open of `open_root_actor()` from within the same process tree
both from a root and sub.
Intro some new `_exceptions` used in the new suite,
- a top level `RuntimeFailure` for generically expressing faults not of
our own doing that prevent successful operation; this is what we now
(changed in this commit) raise on attempts to open a 2nd root.
- mk `ActorFailure` derive from the former; it's already used from
`._spawn` when subprocs fail to boot.
7d537e60cc