Add support for sqlalchemy 2.0 and pydantic 2.11

0.21.0

🐛 Breaking changes

• Drop support for Python 3.8
• Remove the possibility to exclude parents' fields in children models (discouraged as bad practice anyway)
• Add support for Sqlalchemy 2.0 and drop for 1.4

💬 Other

• Bump dependencies to newer versions: among others pydantic, databases and fastapi
• Move setuptools to dev dependencies
• Solve vulnerabilities in dependencies