clan-cli tests: remove dynamic inclusion of helpers module

Dynamically extending the python path at runtime is bad for developer experience, as this is not understood by the text editor and therefore jump to definition etc. does not work.

-> Better to remove the dynamic inclusion and force developers to specify the import correctly.

pkgs/clan-app/tests/conftest.py

@@ -1,14 +1,10 @@
 import subprocess
-import sys
 from pathlib import Path
 
 import pytest
 from clan_cli.custom_logger import setup_logging
 from clan_cli.nix import nix_shell
 
-sys.path.append(str(Path(__file__).parent / "helpers"))
-sys.path.append(str(Path(__file__).parent.parent))  # Also add clan app to PYTHONPATH
-
 pytest_plugins = [
     "temporary_dir",
     "root",