`tests.conftest`: we need a better `daemon` syncing approach, prolly via socket polling

[goodboy]

Per 5b2905b which attempted to get a more reliable daemon registrar startup sync when running tests on macos,

There's a very sloppy registrar-actor-bootup syncing approach used
in this fixture (basically just guessing how long to sleep to wait
for it to init and bind the registry socket) using a global _PROC_SPAWN_WAIT that needs to be made more reliable. But, for now
i'm just playing along with what's there to try and make less CI runs
flaky by,

• sleeping another 1s when run from non-linux CI.
• reporting stdout (if any) alongside stderr on teardown.
• not strictly requiring a proc.returncode == -2 indicating successful
  graceful cancellation via SIGINT; instead we now error-log and only
  raise the RTE on < 0 exit code.
  • though i can't think of why this would happen other then an
    underlying crash which should propagate.. but i don't think any test
    suite does this intentionally rn?
  • though i don't think it should ever happen, having a CI run
    "error"-fail bc of this isn't all that illuminating, if there is
    some weird .returncode == 0 termination case it's likely not
    a failure?

For later, see the new todo list; we should sync to some kind of "ping"
polling of the tpt address if possible which is already easy enough for
TCP reusing an internal closure from ._root.open_root_actor().