add pytest-xdist to test dependencies

This allows you to run tests with `-n auto` flag to start up workers and significantly speed up testing

pyproject.toml

@@ -67,7 +67,7 @@ dependencies = [
 # extras
 # https://peps.python.org/pep-0621/#dependencies-optional-dependencies
 [project.optional-dependencies]
-test = ["pytest", "pytest-cov", "pytest-lazy-fixtures"]
+test = ["pytest", "pytest-xdist", "pytest-cov", "pytest-lazy-fixtures"]
 dev = [
     "black",
     "mypy",