feat: Add LoaderConfig defaults, align CI linting, and update examples

[vndv]

• introduce LoaderConfig and default_config usage to reduce arg noise in loaders
• export LoaderConfig from the package for example usage
• update examples to rely on LoaderConfig and fix sys.path for imports
• restructure optional examples; verify advanced scenarios flow
• set Ruff config source to pyproject in pre-commit; simplify lint job to Ruff on 3.11
• add pytest/coverage artifacts upload in CI and ensure lint uses pyproject settings