Pysaml2

- Include the XSD of the XML Encryption Syntax and Processing Version 1.1 to the schema validator

- deps: restrict pyOpenSSL up to v24.2.1 until it is replaced
- deps: update dependncies for the lockfile and examples

- Fix missing requested attributes from the ACS
- Add support for errorURL to be exposed in metadata for IdP
- Update logged message when the signature validation on the assertion fails
- Replace imp with importlib
- deps: restrict xmlschema version
- deps: remove utility from packaging
- examples: update code and README to align with latest code
- docs: update readme with info about xmlsec1 compatibility

- Add support for xmlsec1 1.3.x
- Use the set crypto_backend when creating the entity metadata

- Fix subject-id requirements processing

- Ensure the ID of each Signature element is unique when signing an encrypted assertion
- Bump Python to 3.9
- dev: Add mypy configuration and type stubs
- tests: move tox.ini config into pyproject.toml
- docs: Update release instructions