feat: add pyats_common directory auto-discovery to PYTHONPATH

[oboehmer]

Add find_pyats_common_parent() function to automatically locate and include pyats_common directories in the test PYTHONPATH. This enables test files to import shared utilities from pyats_common modules.

This way we can use a simpler import path in the architecture-specific python tests:

- from templates.apic.test.pyats_common.apic_base_test import APICTestBase
+ from pyats_common.apic_base_test import APICTestBase

[aitestino]

Superseded by the creation of the nac-test-pyats-common external package, which provides a superior solution to the import path problem.

Resolution:
Instead of auto-discovering local pyats_common directories, we created a centralized pip package that all architecture repos import from:

• Repository: https://github.com/netascode/nac-test-pyats-common
• PyPI Package: nac-test-pyats-common
• Integrated in: nac-test v1.1.0b1

Architecture repos now use standard imports:

from nac_test_pyats_common.aci import APICTestBase
from nac_test_pyats_common.sdwan import SDWANManagerTestBase
from nac_test_pyats_common.catalyst_center import CatalystCenterTestBase

Related:

• Resolved by: [Architecture] Centralize PyATS common utilities into dedicated external repository #428
• Note: This does NOT resolve the directory structure constraints described in Allow more flexibility in the test directory structure #408, which remain valid concerns.