feat: Modernize Python packaging and CI/CD infrastructure

[JasperCraeghs]

📦 Build System Modernization

• Replaced setup.py with pyproject.toml (PEP 621)
• Migrated all configuration to pyproject.toml
• Removed setup.cfg (consolidated into pyproject.toml)
• Updated build backend to modern setuptools

🐍 Python Version Support

Version	Before	After	Status
3.7	✅	❌	EOL June 2023
3.8	✅	❌	EOL October 2024
3.9	✅	✅	Supported
3.10	✅	✅	Supported
3.11	❌	✅	New
3.12	❌	✅	New
3.13	❌	✅	New

🚀 CI/CD Improvements

• Updated GitHub Actions to latest versions (v4/v5)
• Modernized build process using python -m build
• Added proper dependency management for deploy job
• Enhanced version detection with fetch-depth: 0

📋 Configuration Consolidation

All tool configurations now live in pyproject.toml:

• pytest configuration
• flake8 linting rules
• check-manifest settings

🔧 Dependency Updates

• setuptools: Minimum version 77.0 (latest stable)
• jira: Updated to >=3.2.0
• mlx.traceability: Updated to >=11.0.0

✅ Testing

• Updated tox.ini for Python 3.9-3.13
• All existing tests should continue to work
• Package structure maintains backward compatibility
• Import paths remain the same: from mlx.jira_traceability import ...

🎯 Benefits

1. Performance: Faster imports (no pkg_resources dependency)
2. Maintainability: Single configuration file, standard tooling
3. Security: Updated dependencies and CI actions
4. Future-proofing: Ready for Python 3.13+ and modern packaging ecosystem
5. Developer Experience: Standard build commands, better error messages

🔍 Migration Guide

For end users: No changes required - the package imports and API remain identical.

For developers:

# Old build process
python setup.py sdist bdist_wheel

# New build process  
python -m build

📚 Standards Compliance

This PR implements the following PEPs:

• PEP 420: Implicit Namespace Packages
• PEP 517: Build System Interface
• PEP 518: Build System Requirements
• PEP 621: Project Metadata in pyproject.toml

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Related: needed by #14