tests: centralize script path setup in conftest.py

Add a pytest-discovered tests/conftest.py for the last30days scripts path and
remove duplicate per-file sys.path.insert boilerplate from tests.

Normalize affected imports to rely on the shared scripts path and remove the
now-unneeded E402 suppressions.

tests/test_subproc.py

@@ -4,13 +4,9 @@ Covers the process-group cleanup path, timeout behavior, success path,
 PID callback wiring, and environment inheritance.
 """
 
-import sys
 import unittest
-from pathlib import Path
 from unittest.mock import patch
 
-sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "scripts"))
-
 from lib import subproc
 
 
@@ -97,6 +93,5 @@ class TestRunWithTimeout(unittest.TestCase):
         self.assertEqual(result.returncode, 0)
         self.assertEqual(result.stdout.strip(), "ok")
 
-
 if __name__ == "__main__":
     unittest.main()