Increase minimum supported Python version

[debonte]

Currently our minimum supported Python version is 3.8. However, 3.8 has been end of lifed. We should increase the minimum version to 3.9, or perhaps even 3.10 given that support for 3.9 ends in October.

All of the recent versions of pre-commit require 3.9+, so this came up when I was testing Copilot's fix in #95.

[balgillo]

3.8 is a pain but we picked it because it's the version on Ubuntu 22 which is still widely used. Though of course eventually people will use newer Linux versions.

[debonte]

3.8 is becoming increasingly annoying as Python tools (ex. the VS Code debugger) drop support for it. I would suggest that we upgrade to 3.10 and declare a new major version (3.1.0 or 4.0.0). Users who are stuck on 3.8 for whatever reason can continue using the 3.0.x releases.