Use `pytest` plugin now exposed by `tractor`

tests/conftest.py

@@ -15,6 +15,12 @@ from piker.service import (
 from piker.log import get_console_log
 
 
+# include `tractor`'s built-in fixtures!
+pytest_plugins: tuple[str] = (
+    "tractor._testing.pytest",
+)
+
+
 def pytest_addoption(parser):
     parser.addoption("--ll", action="store", dest='loglevel',
                      default=None, help="logging level to set when testing")