Graham/fh 496 nix installer incorrectly validates fstab entries (#1338)

* Enable nosuid and noatime.

/nix should not contain suid/setgid binaries in general.
We don't need atime either.
At the time, I think we were wondering if nix-collect-garbage used atime.
It doesn't.

Having atime is a pretty big performance penalty, and macOS mounts most filesytems noatime already.

* Allow filter_map's that can just be .filter, since those are easier to read

* Move the "prelude" into a suffix, which makes writing and updating the fstab a much simpler operation.
  The fstab on macOS, where this is used, appears to handle a suffix comment just fine.
* Stop trying to detect foreign / native fstab entries.
* Generally, cut out a lot of opportunities for failure by implementing this as a straightforward filter and map.

* Make sure the fstab ends with a newline

src/action/macos/create_determinate_nix_volume.rs

@@ -86,7 +86,7 @@ impl CreateDeterminateNixVolume {
                 .map_err(Self::error)?
         };
 
-        let create_fstab_entry = CreateFstabEntry::plan(name.clone(), &create_volume)
+        let create_fstab_entry = CreateFstabEntry::plan(name.clone())
             .await
             .map_err(Self::error)?;