Bugfix/vector subclass

[zebengberg]

This PR fixes a few small bugs.

Fixes

• Ensure the Flight.fuel attribute is preserved for the Flight.filter method.
• Ensure the Fleet.fl_attrs attribute is preserved for the Fleet.filter method.
• Raise ValueError when Flight.sort or Fleet.sort is called. Both of these subclasses assume a custom sorting order that is enforced in their constructors.

Internals

• Make Fuel and its subclasses JetA, SAFBlend, and HydrogenFuel frozen.

Tests

• [x] QC test passes locally (make test)
• [x] CI tests pass

@nickmasson -- FYI, I think this is independent of our API work.

[zebengberg]

Cool 🚀 Will this be released as 0.49.2?

[EDIT] -- disregard below, sorry! I take "independent of our API work" to mean that these changes aren't fixes for the failing 0.49.1 upgrade sitting in pycontrails-api"...

Sorry for the confusion! Originally I was thinking that the fixes here were necessary for work on the API, but I don't think they're actually needed.

You're absolutely right that pycontrails should have more unit tests, and that the API doubles as an integration test. Like you've pieced together, I discover the pycontrails issues fixed in this PR while debugging some other stuff in the API. Typically when this happens, I create a minimal unit test over here to reproduce the issue.

I won't create a new 0.49.2 release yet unless it turns out the API needs these updates.

[zebengberg]

some of these files may have been pre-auto-formatter.

The formatting changes are from black 23.12. A lot of the recent black minor releases have included these sorts of breaking changes.