Drop older Python versions

[masklinn]

• drop 3.8 (EOL sometime this month, 1.0 is unlikely to be released by then)
• drop pypy 3.8 (dropped in 7.3.12 released 2023-06-16: https://pypy.org/posts/2023/06/pypy-v7312-release.html)
• drop pypy 3.9 (dropped in 7.3.17, released 2024-08-28: https://pypy.org/posts/2024/08/pypy-v7317-release.html)

[masklinn]

Done in #217