Adjust for mypy 1.11

[khaeru]

This PR adjust for some type checking failures seen via CI upon the release of mypy 1.11. @glatterf42 identified that both were due to the new checking of arguments to partial().

Also:

• The argument .operator.stacked_bar(…, dims=…) is adjusted to allow stacking 2+ dimensions, with an exception thrown if the argument is invalid. This corrects the appearance of the final plot in westeros_fossil_resource.ipynb, which previously had 'grade' on the ordinate.
• Improve typing of .operator.as_message_df(). A different return type is indicated according to the wrap= argument.
• Commit some changes to the westeros_report tutorial, as presented at the MESSAGE Workshop in June 2024.

How to review

Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation. Type hints only.
• Update release notes.

[glatterf42]

Please note that I've also opened python/mypy#17569 to verify this change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.6%. Comparing base (6b86116) to head (f1504e8).
Report is 33 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #864   +/-   ##
=====================================
  Coverage   95.6%   95.6%           
=====================================
  Files         46      46           
  Lines       4333    4344   +11     
=====================================
+ Hits        4143    4154   +11     
  Misses       190     190           

Files with missing lines	Coverage Δ
message_ix/report/__init__.py	100.0% <100.0%> (ø)
message_ix/report/operator.py	97.5% <100.0%> (+0.2%)	⬆️
message_ix/report/pyam.py	100.0% <100.0%> (ø)
message_ix/tests/report/test_operator.py	100.0% <100.0%> (ø)

[glatterf42]

All tests passing again, looks good to me :)