Metadata is not stored on a per variant basis

[JeanChristopheMorinPerso]

I recently realized that the metadata we stored in the package definition is not done on a per variable basis. This is extremely problematic because rez-pip's installs wheels, which can have different metadata for a given version. The first thing that comes to mind is the URL of the wheel, then if could be the license or whatever else.

This means that the metadata we store in the pip attribute gets overridden every time a new variant is added/installed. This is very bad.

Rez's design is unfortunately playing against us here. There is only a single package definition for a package (keeping in mind that a package is a version and a version can contain variants). There is no native way to store variant specific metadata.