tests: per-xdist-worker project dirs in sp_composite classes

main now runs pytest with -n auto --dist=worksteal; a class-shared
project dir gets wiped by setUpClass on one worker while another
worker's tests are using it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: alongd

arc/scheduler_test.py

@@ -1273,8 +1273,9 @@ class TestSchedulerSpCompositeOrchestration(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
         cls.ess_settings = {'gaussian': ['server1'], 'molpro': ['server2', 'server1']}
+        worker = os.environ.get('PYTEST_XDIST_WORKER', 'master')
         cls.project_directory = os.path.join(
-            ARC_PATH, 'Projects', 'arc_project_for_testing_sp_composite_orch'
+            ARC_PATH, 'Projects', f'arc_project_for_testing_sp_composite_orch_{worker}'
         )
         if os.path.isdir(cls.project_directory):
             shutil.rmtree(cls.project_directory, ignore_errors=True)
@@ -2483,8 +2484,9 @@ class TestSchedulerSpCompositePassthrough(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
         cls.ess_settings = {'gaussian': ['server1'], 'molpro': ['server2', 'server1']}
+        worker = os.environ.get('PYTEST_XDIST_WORKER', 'master')
         cls.project_directory = os.path.join(
-            ARC_PATH, 'Projects', 'arc_project_for_testing_sp_composite_passthrough'
+            ARC_PATH, 'Projects', f'arc_project_for_testing_sp_composite_passthrough_{worker}'
         )
         cls.spc = ARCSpecies(label='H2', smiles='[H][H]')