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.

scripts/editable-installs/setup_cfg_editable/.gitignore

@@ -0,0 +1,2 @@
+# Artifacts from the build process.
+*.egg-info/

scripts/editable-installs/setup_cfg_editable/setup.cfg

@@ -0,0 +1,3 @@
+[metadata]
+name = setup-cfg-editable
+version = 0.0.1

scripts/editable-installs/setup_cfg_editable/setup.py

@@ -0,0 +1,8 @@
+from setuptools import setup
+
+setup(
+    install_requires=[
+        "requests",
+        'importlib-metadata; python_version<"3.10"',
+    ],
+)

scripts/editable-installs/setup_py_editable/.gitignore

@@ -0,0 +1,2 @@
+# Artifacts from the build process.
+*.egg-info/

scripts/editable-installs/setup_py_editable/setup.py

@@ -0,0 +1,9 @@
+from setuptools import setup
+
+setup(
+    name="setup-py-editable",
+    version="0.0.1",
+    install_requires=[
+        "httpx",
+    ],
+)