chore: rename `ProjectModel` to `PackageModel`

[Hofer-Julian]

trafficstars

While browsing the source code, @tdejager and I found that ProjectModel is a pretty confusing name, since:

• We don't have projects anymore, but workspaces
• It's also not the data of the workspace, but rather data specific to one package

We propose to rename it to PackageModel

AI disclosure

Nearly all of it is generated by codex

[Hofer-Julian]

Should we also remove the version suffix?

Maybe? What was the original idea to have them?

[baszalmstra]

Excellent question. Initially we negotiated the version using the protocol itself. That meant that the protocol types had to support multipe versions. Now that we use a package version for this I think we can greatly simplify this.

[tdejager]

We still need something like it if we want to support a range of build api versions in pixi right?

[baszalmstra]

Yes, we currently define a lower and upper limit of versions. The types in the crate should support those.