3203: support ordering magic methods for `#[pyclass]` r=adamreichold a=davidhewitt
Closes#2089
This adds `__lt__`, `__le__`, `__eq__`, `__ne__`, `__gt__`, and `__ge__` as per the Python implementations of what we call `__richcmp__`.
There's a UI test confirming that the user cannot implement split forms and `__richcmp__` simultaneously.
There's also a benchmark comparing implementing these split methods against using `__richcmp__`. I couldn't see a meaningful performance difference, so I'm tempted to deprecate `__richcmp__`, given that's not a magic method which exists in Python. Potentially we can provide options such as the opt-in `#[pyclass(eq, ord)]` to avoid boilerplate for people who don't want to implement six different methods.
Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>
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