An io/fs.FS implementation for Upspin

[Rodrigo Schio]

Hi folks, I created the upspinfsys module that permit you use Upspin as a fs.FS interface.

This could be useful to serve Upspin with http.FileServer or to use the new go 1.22 functions like zip.Writer.AddFS.

This is the repo:

https://github.com/rschio/upspinfsys