Include `outPaths` of all the `outputs` of a derivation

[shivaraj-bh]

getDrv relies on nix’s derivation-to-string-coercion that only returns the path to $out.

In some cases, like when enableSeparateIntermediatesOutputs is used for incremental builds in a Haskell package, the $intermediates output is missed by devour-flake.

[srid]

Sounds good to me.

This would require a corresponding omnix change, right?