[Cython] Annotations and Cython 3

[da-woods]

I suspect the answer to this is still "wait and see" but: do we have an 
opinion on what we want to do about annotations in Cython 3.

Currently we're targetting PEP-563 behaviour. To me it looks fairly 
likely that this won't be what Python decides on. I guess the likely 
outcomes are "status quo" or something close to PEP-649.

The issue with the PEP-563 (stringify everything) behaviour is that it's 
noticeably different, so releasing Cython 3 with that behaviour then 
changing to something else will be an obvious incompatible change.

I'd be reluctant to implement PEP-649 until it's actually accepted (it 
looks hard...). Is it worth reverting to the Cython 0.29 behaviour (with 
some scoping fixes) on the basis that it's what most people are using 
now, and it's likely to be closer what what's picked?

Or should we at least mark "decide what to do with annotations" as a 
blocker for Cython 3?

David