import: crate: Add recursive import test.

* tests/crate.scm (test-crate): Rename to...
(test-foo-crate): ... this.
(test-dependencies): Rename to...
(test-foo-dependencies): ... this.
(test-root-crate, test-root-dependencies, test-intermediate-1-crate)
(test-intermediate-1-dependencies, test-intermediate-2-crate)
(test-intermediate-2-dependencies, test-leaf-alice-crate)
(test-leaf-alice-dependencies, test-leaf-bob-crate)
(test-leaf-bob-dependencies): New variables.
("crate->guix-package"): Adjust accordingly.
("cargo-recursive-import"): New test.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>