Automatically detect workspace packages in `uv add` (#4557)
## Summary
If the package _isn't_ marked as `workspace = true`, locking will fail
given:
```rust
let workspace_package_declared =
// We require that when you use a package that's part of the workspace, ...
!workspace.packages().contains_key(&requirement.name)
// ... it must be declared as a workspace dependency (`workspace = true`), ...
|| matches!(
source,
Some(Source::Workspace {
// By using toml, we technically support `workspace = false`.
workspace: true,
..
})
)
// ... except for recursive self-inclusion (extras that activate other extras), e.g.
// `framework[machine_learning]` depends on `framework[cuda]`.
|| &requirement.name == project_name;
if !workspace_package_declared {
return Err(LoweringError::UndeclaredWorkspacePackage);
}
```
Closes https://github.com/astral-sh/uv/issues/4552.
