add requires-python field in pyproject toml

[ismael-mendoza]

We were missing this field in our pyproject.toml.

I left it at 3.11 although we could consider 3.12 looking at SPEC (https://scientific-python.org/specs/spec-0000/)

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 36 untouched benchmarks

---

_{Comparing add-requires-python (b969318) with main (1977814)}