bug#40895: import crate: Relaxed version selection

[Hartmut Goebel <h.goebel@crazy-compilers.com>]

If (manually) importing dependencies for some package requiring "other
^0.2", I would like the importer to fetch the newest version of
other-0.2.x automatically.

As it is now, I need to specify the exact version number, e.g. "guix
import crate other@0.2.4" - and the get the version number I need to go
to crates.io, search the package and search the list of available
versions. The importer can do this much more efficient.

This could be implemented like this:

- If the version giben ("@0.2.4") matches an version available, use this
version.

- Otherwise, if the version giben ("@0.2") is a prefix of some available
version, use the highest/newest of these versions

-- 
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
| www.crazy-compilers.com | compilers which you thought are impossible |