For ECOC2026-Add end-to-end tests for NBI → Pluggables → SBI and pluggable management

- Implemented a comprehensive test suite for NBI to Pluggables to SBI interactions, focusing on NETCONF devices.
- Created `test_nbi_pluggable_sbi.py` to validate the full lifecycle of pluggables including creation, configuration, deletion, and state verification.
- Added tests for ensuring the correct topology is loaded and devices are managed properly.
- Introduced `test_pluggable_ecoc_flow.py` to cover various scenarios for pluggable creation, configuration, and error handling.
- Included logging for better traceability during test execution.
- Ensured cleanup of test environment to maintain isolation between test runs.