feat(python): add unit tests and remove hardcoded credentials

[57388sp]

Summary
Add a comprehensive unit test suite for all Python scripts and remove all
hardcoded credentials and environment-specific values.

Changes

Unit tests (new)

• Unit_tests - 142 tests covering all 9 scripts + OntapClient
• pytest.ini - test configuration
• requirements-dev.txt - dev/test dependencies

Python scripts

• Cleared from all INPUTS/ENV blocks: IP addresses, passwords, SVM names,
  volume names, aggregate names - all must now be supplied via environment variables
• Refactored ontap_client.py: _DEFAULT_TIMEOUT=90, added poll_job(),
  wait_snapmirrored(), load_env_file(), update_auth(), __all__
• Reduced cyclomatic complexity - all functions A/B grade (radon)
• Fixed non-ASCII characters in comments
• Added type hints and docstrings to all public functions

Quality gates

• ruff check python/ Unit_tests/ - 0 warnings
• pytest Unit_tests/ -q - 142 passed

Security

• No credentials, IPs, or environment-specific values remain in source files
• All sensitive inputs must be provided via os.environ or the INPUTS/ENV
  dict at runtime

[github-actions]

Test Report

Environment: N/A - this PR does not add or modify a runnable example.
It adds unit tests and removes hardcoded credentials from existing scripts.

The changes in this PR are:

1. Removal of hardcoded credentials/IPs from INPUTS/ENV blocks (no
   behaviour change - scripts work identically, values come from env vars).
2. Addition of Unit_tests - these are mock-based unit tests that run
   without a cluster.

Unit test run (first run):

python -m pytest Unit_tests/ -q
............................................................... [ 40%]
............................................................... [ 80%]
................................................................[100%]
142 passed in 0.30s