Fix for projective curve pickling, enabling more tests for function field Jacobians

[vincentmacri]

Fixes a pickling issue I encountered while working on some function field improvements. This lets us enable some additional tests for Jacobians of function fields that were disabled due to a pickling issue with projective curves.

Previously the _open_affine and _map_from_function_field properties of projective curves would fail to pickle. We solve this by not storing them in the pickle since they are easy to recompute.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[kwankyu]

LGTM. Would you merge develop to test?

[github-actions]

Documentation preview for this PR (built with commit 0f91b6d; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[vincentmacri]

Test failures are unrelated as far as I can tell. @kwankyu anything else?

[kwankyu]

.. @kwankyu anything else?

No. Thanks.

[vincentmacri]

Thanks for the review!