chore: add docstrings and ruff noqa directives to test files

Add module-level docstrings and ruff: noqa: E402 directives to all test files to suppress import order warnings.

Author: kenryu42

tests/test_concurrency.py

@@ -1,3 +1,7 @@
+"""Concurrency-related tests."""
+
+# ruff: noqa: E402
+
 import io
 import json
 import os

tests/test_export_plan.py

@@ -1,3 +1,7 @@
+"""Tests for scripts/export_plan.py."""
+
+# ruff: noqa: E402
+
 import io
 import json
 import sys

tests/test_export_project_plans.py

@@ -1,3 +1,7 @@
+"""Tests for scripts/export_project_plans.py."""
+
+# ruff: noqa: E402
+
 import json
 import os
 import sys

tests/test_export_project_plans_with_timestamp.py

@@ -1,3 +1,7 @@
+"""Tests for scripts/export_project_plans_with_timestamp.py."""
+
+# ruff: noqa: E402
+
 import json
 import os
 import sys

tests/test_session_start.py

@@ -1,3 +1,7 @@
+"""Tests for scripts/session_start.py."""
+
+# ruff: noqa: E402
+
 import io
 import json
 import os