Support workspace to workspace path dependencies (#4833)

Add support for path dependencies from a package in one workspace to a
package in another workspace, which it self has workspace dependencies.

Say we have a main workspace with packages `a` and `b`, and a second
workspace with `c` and `d`. We have `a -> b`, `b -> c`, `c -> d`. This
would previously lead to a mangled path for `d`, which is now fixed.

Like distribution paths, we split workspace paths into an absolute
install path and a relative (or absolute, if the user provided an
absolute path) lock path.

Part of https://github.com/astral-sh/uv/issues/3943

crates/uv-requirements/src/source_tree.rs

@@ -172,7 +172,8 @@ impl<'a, Context: BuildContext> SourceTreeResolver<'a, Context> {
         };
         let source = SourceUrl::Directory(DirectorySourceUrl {
             url: &url,
-            path: Cow::Borrowed(source_tree),
+            install_path: Cow::Borrowed(source_tree),
+            lock_path: Cow::Borrowed(source_tree),
             editable: false,
         });