[Python] Release 0.52.0

Added

• The offline argument, refusing to fetch references outside registry.

Fixed

• Canonicalization not idempotent where a patternProperties $ref matches a key properties names.
• Type stubs omitting ValidationError.absolute_keyword_location.
• The draft argument and the Draft201909Validator / Draft202012Validator classes gating keywords on the vocabularies of the $schema they override, so the validator accepted every instance.
• is_valid disagreeing with validate, iter_errors, and evaluate on a schema that reaches its own $ref twice, one of them under not.