FW-735: Pipeline failing - changes to Enum class in Python 3.12.10

[richjam]

It looks like 3.12.10 included some updates to the Enum class that is causing a new TypeError when setting up a new BitwiseFlag class.

See changelog: https://docs.python.org/release/3.12.10/whatsnew/changelog.html#python-3-12-10

Specifically: gh-108682: Enum: require names=() or type=... to create an empty enum using the functional syntax.
python/cpython#108682

Looks like stricter validation introduced in the enum module. Specifically, when instantiating an enumeration, Python now raises a TypeError if the class has no members defined. This change was implemented to prevent the creation of empty Flag enumerations without explicitly specifying that intention.

In our implementation, overriding the __new__ class method, was interfering with how members are registered during enum class creation and leading to the above type error.

Looks like fix is to just move validation done in __new__ to a new place (__init_subclass__).

Note
This error was introduced in the Github pipeline, but was not showing up when running locally. Github was using the latest 3.12.10 Python release, whereas locally, was still using 3.12.3 (the latest version available in the apt deadsnakes ppa).

Had to install 3.12.10 locally by building the binaries manually.

[joncooper65]

LGTM - and good to learn about init_subclass(cls, **kwargs) and how it affects validation on instantiation - ie having to explicitly iterate over the enum's members.