`audioop` removed for `python_version >=v3.13`

I have noticed sf2utils wan't working from a pip install for python version 3.13 as audioop has been deprecated and removed as a standard library.

This could be fixed using the audioop_lts dependency for later python versions, i.e. in pyproject.toml:

[tool.poetry.dependencies]
audioop-lts = { version = "...", python = "^3.13" }

see here for more info: https://pypi.org/project/audioop-lts/