Add support for unnamed local directory requirements (#2571)

## Summary

For example: `cargo run pip install .`

The strategy taken here is to attempt to extract the package name from
the distribution without executing the PEP 517 build steps. We could
choose to do that in the future if this proves lacking, but it adds
complexity.

Part of: https://github.com/astral-sh/uv/issues/313.

crates/pypi-types/src/metadata.rs

@@ -210,6 +210,30 @@ impl Metadata23 {
     }
 }
 
+/// Python Package Metadata 1.0 and later as specified in
+/// <https://peps.python.org/pep-0241/>.
+///
+/// This is a subset of the full metadata specification, and only includes the
+/// fields that have been consistent across all versions of the specification.
+#[derive(Serialize, Deserialize, Debug, Clone, Eq, PartialEq)]
+#[serde(rename_all = "kebab-case")]
+pub struct Metadata10 {
+    pub name: PackageName,
+}
+
+impl Metadata10 {
+    /// Parse the [`Metadata10`] from a `PKG-INFO` file, as included in a source distribution.
+    pub fn parse_pkg_info(content: &[u8]) -> Result<Self, Error> {
+        let headers = Headers::parse(content)?;
+        let name = PackageName::new(
+            headers
+                .get_first_value("Name")
+                .ok_or(Error::FieldNotFound("Name"))?,
+        )?;
+        Ok(Self { name })
+    }
+}
+
 /// Parse a `Metadata-Version` field into a (major, minor) tuple.
 fn parse_version(metadata_version: &str) -> Result<(u8, u8), Error> {
     let (major, minor) = metadata_version