Add support for Hatch's {root:uri} paths in editable installs (#2492)

## Summary

If a package uses Hatch's `root.uri` feature, we currently error:

```toml
dependencies = [
  "black @ {root:uri}/../black_editable"
]
```

Even though we're using PEP 517 hooks to get the metadata, which
_should_ support this. The problem is that we load the full
`PyProjectToml`, which means we parse the requirements, which means we
reject what looks like a relative URL in dependencies.

Instead, we should only enforce a limited subset of `pyproject.toml`
(arguably none).

Closes https://github.com/astral-sh/uv/issues/2475.

crates/uv/tests/pip_compile.rs

@@ -5150,3 +5150,39 @@ requires-python = "<=3.8"
 
     Ok(())
 }
+
+/// Build an editable package with Hatchling's {root:uri} feature.
+#[test]
+fn compile_root_uri() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("-e ${ROOT_PATH}")?;
+
+    // In addition to the standard filters, remove the temporary directory from the snapshot.
+    let filters: Vec<_> = [(r"file://.*/", "file://[TEMP_DIR]/")]
+        .into_iter()
+        .chain(INSTA_FILTERS.to_vec())
+        .collect();
+
+    let root_path = current_dir()?.join("../../scripts/editable-installs/root_editable");
+    uv_snapshot!(filters, context.compile()
+        .arg("requirements.in")
+        .env("ROOT_PATH", root_path.as_os_str()), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by uv via the following command:
+    #    uv pip compile --cache-dir [CACHE_DIR] --exclude-newer 2023-11-18T12:00:00Z requirements.in
+    -e ${ROOT_PATH}
+    black @ file://[TEMP_DIR]/black_editable
+        # via root-editable
+
+    ----- stderr -----
+    Built 1 editable in [TIME]
+    Resolved 2 packages in [TIME]
+    "###
+    );
+
+    Ok(())
+}