Python version for seastar-addr2line

[travisdowns]

What is the Python version requirement for seastar-add2line?

Evidently it requires at least Python 3.6 since it uses f-strings, but I'm not sure beyond that.

I'd like to make some enhancements, e.g., type annotations but would need to know if say targeting Python 3.9 (released 8 years ago) is alright.