SKETCH: Drop build constraints for python 3.9+

[adrianeboyd]

Description

The use of build-constraints.txt is an explosion-internal design intertwined with wheelwright. After dropping python 3.8, the oldest-supported-numpy-ish build constraints are no longer necessary, which greatly simplifies the cibuildwheel setup, making it much more feasible/sensible to move wheel building into a repo-internal workflow rather than using wheelwright.

All of the complicated settings related to PIP_CONSTRAINT can be removed from the cibuildwheel settings and you can switch to the build frontend to have more isolated builds. (I thought this would eliminate the need for the clean step for profiling-free python 3.12 builds, but it didn't seem to work in my initial tests.)

wheelwright sketch:

https://github.com/explosion/wheelwright/tree/branch-for-spacy-3899e82e6

ec2buildwheel sketch:

https://github.com/explosion/ec2buildwheel/tree/drop-build-constraints

Resulting wheelwright build:

https://dev.azure.com/explosion-ai/Public/_build/results?buildId=26889&view=results

Types of change

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Checklist

• [ ] I confirm that I have the right to submit this contribution under the project's MIT license.
• [ ] I ran the tests, and all new and existing tests passed.
• [ ] My changes don't require a change to the documentation, or if they do, I've added all required information.