bencode: drop support for go 1.20

[vassilit]

No description provided.

[anacrolix]

I appreciate the tidy up, but I prefer to make it easier to backport if needed, rather than tighten the constraints, at least for something like this that has no runtime or compile time overhead.

[vassilit]

I wouldn't have tidied up either it if it wasn't for commit e10ffd1 « Drop support for Go 1.20 ».
I thought you forgot to clean up here as well :)

[anacrolix]

Yeah it was more that it's a hassle to guarantee backward compatibility, but I don't want to throw it away.

Your contributions are welcome, thanks for the consideration.