Fix SolutionInform dict access

[ewu63]

Purpose

Created from #450.

Realized that we effectively broke sol_inform in #437 because we were previously using a dict. This is now fixed by implementing __getitem__, and I think we should just make a patch release ASAP, this oversight is probably going to break pretty much everyone's code...

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

[marcomangano]

Good catch, the test looks good

[eirikurj]

Little late to this, but do we want to add some deprecation warning here when accessing as a dict? In general, we could keep both features for accessing data, but I think the dataclass access is superior and the correct application here compared to the dict. Thus, we should consider removing the dict referencing in a future version. Let me know what you think.

[whophil]

Also late to the party here, but what about TypedDict?

[ewu63]

So @eirikurj to get to your question from the other thread, I'm pretty sure anyone who wants to access the exit code (and many people presumably would) uses sol.optInform which previously was a dict and now is a dataclass, so it is a major breaking change IMO. In any case this PR patches it OK, I can add the deprecation warnings as suggested.

@whophil I'm not sure if a TypedDict will do anything better, since we already moved to a dataclass format which is probably a little cleaner, and I'm not sure if we can use TypedDict to patch the compatibility somehow.