MAINT: Drop Python 3.9 support, require Python 3.10 (following SPEC 0)

[EwoutH]

NEP 29 was superseded by the scientific python ecosystem coordination guideline SPEC 0 — Minimum Supported Versions. Where NEP had a 42 month support windows (3.5 years) for each Python version, SPEC 0 recommends a 3 year support window.

If we were to follow SPEC 0, than Python 3.9 support can already be dropped, since it was released October 5th, 2020.

Requiring Python 3.10+ for future NumPy releases would allow to start use Structural Pattern Matching and new typing features. See What’s New In Python 3.10.

[jakirkham]

This appears to have happened in PR: #58238

Should this be closed?

[mroeschke]

Yup. Closing