Drop python 3.8 support

[manulera]

Biopython has dropped python 3.8 support in their last release, so we won't be able to use the latest version until we drop it as well.

I would say this is probably fair in 2025, let me know what you think. In the mean time, I will see if I can fix #337

[manulera]

I am thinking we could also pin a particular biopython version rather than >= something. In the end we depend so much on their methods that if anything changes (clearly it does) it may be problematic.

[BjornFJohansson]

i agree to drop 3.8 and also to pin the biopython versions with more granularity.
Pydna is especially sensitive to changes in the Bio.Seq module.
They changed the Bio.Seq data property to bytestring between 1.78 and 1.79,
so biopython = ">=1.80,<=1.85" should work.
I don't remember right now if 1.79 also works.

[manulera]

This is already done in #340