investigate/develop a buildInputs setup hook to resholve all outputs of a Nix build

[abathur]

@grahamc pointed out that resholved may also be helpful as a Nix setup hook.

I think this is a natural progression (and will probably be a good stress test). I'm a little unsure what this should look like, so I'm optimistic it'll be a straightforward contribution for someone with a little more perspective than I have on the Nix ecosystem.

A few mixed thoughts:

1. It might be useful, performance wise, to avoid eagerly resolving some things things? (wrappers, nix-shell scripts, shebangless scripts with a .sh extension, multiple scripts that all symlink to a single file and use $0 to execute differently)

2. I don't have any sense from a distance how configurable the hook interface needs to be. If these tasks rarely require overrides or special settings, it may be trivial to implement this at any time. If it needs to be able to customize significantly, we'll need to be a little more intentional about the interface (and it would probably be best to do that alongside the QC pass on the existing APIs.)