bug#71360: large manifests when adding packages

[Dariqq <dariqq@posteo.net>]

Hi Guix,

I was trying to figure out if the "repeated" tag inside a profiles 
manifest file is reliable to detect duplicate entries in a profile. 
While it was working fine for my home and system profile for the normal 
.guix-profile it was not:

This is related to https://issues.guix.gnu.org/55499#0 resp. 
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=4ff12d1de7cd617b791996ee7ca1240660b4c20e 
which marks duplicate entries in a profiles as repeated inside the 
profile manifest file.

* Steps to reproduce

To stick with the original example: Instead of adding the r packages all 
in one add them one by one

#+begin_example
guix package -p /tmp/wrong -i r-cicero-monocle3
guix package -p /tmp/wrong -i r-monocle3
#+end_example

The resulting manifest file at /tmp/wrong/manifest has the huge tree for 
r-monocle3 twice.

So the lookup mechanism in manifest->gexp does not seem to work with the 
install mechanism of profiles. I haven't looked more deeply into it yet.

An smaller example is using zlib and glib (which propagates zlib).

* Expected Behaviour

It should not matter whether you install things in multiple transactions 
or in one.

Thanks.