build: Drop python 3.7

[tlambert03]

v0.9.x will be the last version range to support python 3.7

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (d3d558d) 99.89% compared to head (0984356) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #268 +/- ## =========================================== + Coverage 99.89% 100.00% +0.10% =========================================== Files 22 22 Lines 1908 1849 -59 =========================================== - Hits 1906 1849 -57 + Misses 2 0 -2 ```

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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #268 will not alter performance

_{Comparing tlambert03:drop-37 (0984356) with main (d3d558d)}

Summary

✅ 66 untouched benchmarks