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_youtube_yt.py

@@ -2,15 +2,11 @@
 
 import json
 import os
-import sys
 import tempfile
 import unittest
 import urllib.error
-from pathlib import Path
 from unittest import mock
 
-sys.path.insert(0, str(Path(__file__).parent.parent / "skills" / "last30days" / "scripts"))
-
 from lib import youtube_yt
 
 
@@ -536,6 +532,5 @@ class TestYtdlpSSHRouting(unittest.TestCase):
         self.assertIn("--ignore-config", cmd[5])
         self.assertIn("--no-cookies-from-browser", cmd[5])
 
-
 if __name__ == "__main__":
     unittest.main()