Add details about derivation realisations

[GuillaumeDesforges]

Currently, we extract information about evaluated derivation. In many cases, it's useful to know about the realisation (see nix-store --realise).

This includes, but is not limited to:

• build success
• list of files in the output (related to #12)
• size of output (related to https://github.com/tweag/nixpkgs-graph-explorer/issues/23#issuecomment-1549276282)
• existence in cache and size of archive
• closure size (what is the biggest dependency of package X?)

Please mention other data of interest.

This data can be fetched from many places, I guess most of it should be available directly in Hydra.

[GuillaumeDesforges]

We'll do that on a per-feature basis, e.g. "display the detail of a closure size"