`cabal get` all packages in cabal file

**Describe the feature request**
Run `cabal get` on all `build-depends` and place in target directory.

**Additional context**
I want to use `ctags` to jump to definition on non-project functions. Thus, one would `cabal get` everything and run a `ctags` generator on that directory.

I am sure there is a way to do this with the API already, but this package is massive and discovering the right functionality for this is tricky. There used to be a tool called `codex` [[repo]](https://github.com/aloiscochard/codex?tab=readme-ov-file) (unmaintained) that did this, but it was deprecated, presumably because this functionality is now native somewhere here.

_cabal unpack_

Start by tracing the existing `cabal get` and `cabal unpack` command behavior and looking for the API that resolves and retrieves package sources. Define completion as retrieving all packages named in `build-depends` and placing their sources in the requested target directory, with behavior suitable for running `ctags` there.

Written by the indexing model from the issue text.