file.Sync is not implemented

[wmcnamee-coreweave]

I was interested in atomic file writes using Billy interface, but I found that file.Sync method is not implemented.

e.g.

https://github.com/google/renameio/blob/master/tempfile.go#L150
https://github.com/tailscale/tailscale/blob/main/atomicfile/atomicfile.go#L44
https://github.com/natefinch/atomic/blob/master/atomic.go#L43

https://pkg.go.dev/os#File.Sync

Can this be implemented or a helper function added?

[pjbgf]

@wmcnamee-coreweave we should be able to add support to it on both osfs implementations. But we won't be able to add it to the billy.Filesystem interface, due to the Liskov Substitution Principle.

Feel free to propose a PR for this.