I assume the reason these aren't all individual tests is test-time but
if we divide by success/failure, I'll need to duplicate things to handle
partial versions.
Overall, I feel like this makes the tests make more sense.
In addition to `foo:1.2.3`, we now support `foo@1.2.3` for pkgids. We
are also making it the default way of rendering pkgid's for the user.
With cargo-add in #10472, we've decided to only use `@` in it and to add
it as an alternative to `:` in the rest of cargo. `cargo-add`
originally used `@`. When preparing it for merge, I switched to `:` to
be consistent with pkgids. When discussing this, it was felt `@` has
precedence in too many tools to switch to `:` but that we should instead
switch pkgid's to use `@`, in a backwards compatible way.
See also https://internals.rust-lang.org/t/feedback-on-cargo-add-before-its-merged/16024/26?u=epage
