Fixes issue where register_api isn't idempotent

[zakmatik]

In a situation where we may instantiate multiple apps that register the same blueprint, this change updates register_api to always update the APIBlueprint's instance variables to the same values no matter how many times it is invoked.

Checklist:

• Run pytest tests and no failed.
• Run ruff check flask_openapi3 tests examples and no failed.
• Run mypy flask_openapi3 and no failed.
• Run mkdocs serve and no failed.

For the fix here, I opted to update an additional field in the api rather than not updating the API because I thought that it would be helpful to have the proper updated api.paths field. I'm open to other approaches as well!

[luolingchun]

@zakmatik Thank you for your contribution, but register_api_view need this logic as well.

[zakmatik]

@luolingchun Thanks for the heads up! I went ahead and also implemented for APIView and added another test. Not sure if eventually it makes sense to refactor those functions into a single "path calculation" function, but for now I kept it simple and just updated both places.