Feature request: package ID specification

[LukeMathWalker]

It is possible to access the PackageId attached to each crate in a workspace via guppy, but I can't see any functionality to generated a valid package ID specification starting from that PackageId (or, more likely, its PackageMetadata.

This would be quite convenient when having to issue other cargo commands!

[sunshowers]

Hi -- I've left Meta and can no longer contribute to this repository. Please file an issue at guppy-rs/guppy. Thanks.