Pydantic 2 support - is_classvar

[ashupednekar]

Is your feature request related to a problem? Please describe. I'm only trying to use the class based views from this library. In order to support pydantic 2

Describe the solution you'd like I understand that there are other open PR's addressing pydantic 2 support. Since I'm only trying to use cbv decorator for class based view, I would like the is_classvar issue to be fixed first, so that it can be used in conjunction with pydantic 2, while the rest of the fixes are being developed.

Describe alternatives you've considered If this PR is not merged, I would continue to use a fork internally, till #276 is merged

Additional context We're migrating from Django rest to fastapi... so class based views are a must for us. I'm building out essential functionalities from DRF, so that we can retain the structured and maintainable code base we already have