Switch to cyipopt

[ewu63]

Purpose

Closes #374, and hopefully addresses some of the issues we've been having. I also added the long-awaited numpy2 test on CI (with windows).

Some to dos:

• decide whether we want to specify cyipopt as a dependency
• check options, setups, etc. to cyipopt and compare against previous code
• update documentation

Expected time until merged

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation