Deprecate use of positional arguments in CyIpopt callbacks

[blnicho]

Summary

This idea is from a discussion on PR #3289. We want to be able to support CyIpopt callbacks with either 12 or 13 arguments but it can be confusing how many arguments are required in the default case when using positional arguments. We should update our CyIpopt callback API to only support named arguments to make things clearer and more future-proof.

(See comments here: #3289 (comment))