Serialize NameID object before writting it in the session object.

[pdelboca]

This PR fixes an issue that occurs because NameID is not a serializable object and therefore we cannot assign it to the session object.

The name_id is not JSON serializable
'name_id': <saml2.saml.NameID object at 0x7fca2256f090>

SecureCookieSession object:

        {
            '_user_id': 'ca876e56-xxx',
            '_fresh': True,
            '_id': '892f7fec2xxxx',
            '_saml_session_info': {
                'ava': {
                    'uid': ['test'], 'email': ['[email protected]'], 'firstname': ['John'],
                    'lastname': ['Smith'], 'fullname': ['John Smith (Operations)'],
                    'eduPersonAffiliation': ['users', 'examplerole1']
                },

               'name_id': <saml2.saml.NameID object at 0x7fca2256f090>,

                'came_from': None,
                'issuer': 'http://idp.example.com/metadata.php',
                'not_on_or_after': 1926493308,
                'authn_info': [
                    ('urn:oasis:names:tc:SAML:2.0:ac:classes:Password', [], '2025-01-14T20:06:00.934671')
                ],
                'session_index': '_be9967abd904ddcae3c0eb4189adbe3f71e327cf93'
            },
            '_saml2_subject_id': '1=urn%3Agov%3Agsa%3ASAML%3A2.0.profiles%3Asp%3Asso%3Atest%3Aentity,2=urn%3Aoasis%3Anames%3Atc%3ASAML%3A2.0%3Anameid-format%3Atransient,4=_ce3d29xxx'
        }

[avdata99]

I'll merge to test loclly with my changes