CMLDEV-1069 Enable ruff linting in PCL, replace flake8/isort/black

[marpauli-cisco]

Summary:

• Add comprehensive ruff configuration to pyproject.toml reusing the monorepo core rule set with PCL-appropriate overrides
• Fix all 52 ruff violations across source and test files
• Replace flake8/isort/black with ruff in CI and pre-commit hooks

Changes:

Config (pyproject.toml):

• Add [tool.ruff] with rule selection (E, W, F, I, PL, S, B, UP, N, SIM, C4, A, RUF, G, T20), ignore set, per-file-ignores for tests and API-driven constructors, isort and format settings
• Replace flake8 dev dependency with ruff

Source (virl2_client/):

• Add ClassVar annotations to mutable class-level dicts (_URL_TEMPLATES, _ERROR_PREFIX) across 15 model files

Tests (tests/):

• Collapse nested with statements (SIM117) across 12 test files
• Escape regex metacharacters in pytest.raises(match=...) patterns (RUF043)
• Fix collapsible if statements (SIM102), blind pytest.raises(Exception) (B017), function call in default argument (B008), if/else to ternary (SIM108)
• Apply ruff-format fixes to 2 test files

CI & tooling:

• Replace flake8 lint step with ruff check --no-fix + ruff format --check in GitHub Actions
• Remove isort and black hooks from .pre-commit-config.yaml
• Rename legacy ruff hook ID to ruff-check
• Regenerate poetry.lock and tests/requirements.txt

Testing:

• ruff check virl2_client/ tests/ conftest.py — all checks passed
• ruff format --check virl2_client/ tests/ conftest.py — all files formatted
• pytest -n auto — all 1543 tests passing