Improve 'chisel find' to list all missing slices I have to create myself (and dump all available for $my_package)

Hi,

I have $my_package I want to chisel (with 388 apt dependencies):
```
> apt-rdepends $my_package | wc -l
338
```

I had to run 100+ times to find all available slices:
```
> chisel find --release ubuntu-24.04 libuuid1
> chisel find --release ubuntu-24.04 libcap2
...
```

It would be great to have something like:
```
> chisel find --release ubuntu-24.04 --rdepends $my_package --missing
libldap-common
libxxhash0
...
```

the same way it can generate for me list of available slices (moreover if dependency has one slice only):
```
> chisel find --release ubuntu-24.04 --rdepends $my_package --available
libp11-kit0_libs
libffi8_libs
libtasn1-6_libs
...
```

So, I can drag&drop them into my yaml file. Tnx!

Start with the `chisel find` command and its existing `--rdepends` and `--available` behavior; trace how package dependencies and slices are resolved. Done means a new invocation can report every missing slice and list available slices for `$my_package`, with output suitable for the YAML file.

Written by the indexing model from the issue text.