Add type annotations for primary key types by model

[ormsbee]

@ormsbee: fill out details.

[kdmccormick]

This is a type hardening which we'd discussed in Slack. Basically, we'd subtype int into things like ForeignKey[Component] so that mypy can call out cases where you passed in the wrong model's ForeignKey. This is especially important for Learning Core because the APIs generally accept FKs (as an optimization) rather than model instances, data objects, or opaque keys.

I'll let @ormsbee paste in the details.

[kdmccormick]

Implemented by:

• Add type annotations for primary key types by model [FC-0117] #534
• Platform: Add type annotations for primary key types by model [FC-0117] openedx-platform#38308

[bradenmacdonald]

I'm marking this as done now, though I haven't applied typed keys to all our models yet. (e.g. I didn't yet do PublishableEntityVersion, Media, MediaType, ContainerType, tagging models, etc.) If there's any other models you'd like me to change over to use fully typed keys now, just let me know.

[bradenmacdonald]

The new TypedBigAutoField and TypedAutoField are also now available in openedx-platform, to use on any models we'd like there. Maybe once OEP-68 is finalized, we can try to evangelize this a bit among platform devs.

[kdmccormick]

Cool, I made #538 so that we remember to update the OEP. Can be after Verawood, once we've had a chance to use annotations these for a bit.