pySCG: add testing framework for code examples and docs

[tommcd]

Add pytest-based testing framework with 783 test cases to validate Python code examples and Markdown documentation structure.

Features:

• Python validation: syntax, deprecation warnings, expected output
• Markdown validation: required sections, tables, section order, code refs, inlined code sync
• Link validation: internal links, index table, code file references
• Smart CI/CD: tests only changed CWE directories on PRs (~1 min)
• Full suite: runs all tests on pushes to main (~3 min)
• Multi-version: Python 3.9-3.14 testing with tox
• Clean reporting: generate_issue_report.py for actionable summaries
• Auto cleanup: removes test artifacts after test runs

New: Inlined Code Validation

• Validates README inlined code blocks match actual Python files
• Catches outdated documentation when code is updated but README isn't
• Prevents SPDX headers and test markers from appearing in documentation
• Identified 18 files with mismatches (pre-existing issues documented)

CI/CD Integration:

• GitHub Actions workflow with matrix strategy
• Lychee link checker (internal links in CI, external available locally)
• Coverage reporting to Codecov
• Fast execution with uv package manager

Documentation:

• Comprehensive tests/README.md with usage examples
• Updated CONTRIBUTING.md with testing workflow
• KNOWN_ISSUES.md documents 53 files with pre-existing issues

The framework identifies issues in 53 files (35 documentation files with missing sections/tables/order/inlined code issues, 11 Python files with timeouts, 1 with deprecation warning) documented in KNOWN_ISSUES.md. These pre-existing issues can be addressed in follow-up PRs. All new contributions will be validated automatically.

Closes #1010

[codecov]

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[myteron]

Great to see effort invested in cleaning up the codebase and documentation. While we need to do this, I do believe that restructuring and getting the content to a release is more important at the moment.

We can surely come up with a solution that does not require Kiro or any specific IDE. To avoid pushing against a GitHub linter we must have a solution matching local vs GitHub runs. Idealistically we have a matching code style support as on option for an IDE. Keeping this simple will avoid barriers for new contributors to join. We can increase complexity after reaching healthy amount of active contributors.

Rg Helge