Pass Requirement objects around (#12709)

This allows us to keep metadata like python_version and platform_system
and use it to conditionally install packages.

tests/regr_test.py

@@ -139,13 +139,15 @@ def setup_testcase_dir(package: DistributionTests, tempdir: Path, verbosity: Ver
     # mypy refuses to consider a directory a "valid typeshed directory"
     # unless there's a stubs/mypy-extensions path inside it,
     # so add that to the list of stubs to copy over to the new directory
-    for requirement in {package.name, *requirements.typeshed_pkgs, "mypy-extensions"}:
+    typeshed_requirements = [r.name for r in requirements.typeshed_pkgs]
+    for requirement in {package.name, *typeshed_requirements, "mypy-extensions"}:
         shutil.copytree(Path("stubs", requirement), new_typeshed / "stubs" / requirement)
 
     if requirements.external_pkgs:
         venv_location = str(tempdir / VENV_DIR)
         subprocess.run(["uv", "venv", venv_location], check=True, capture_output=True)
-        uv_command = ["uv", "pip", "install", get_mypy_req(), *requirements.external_pkgs]
+        ext_requirements = [str(r) for r in requirements.external_pkgs]
+        uv_command = ["uv", "pip", "install", get_mypy_req(), *ext_requirements]
         if sys.platform == "win32":
             # Reads/writes to the cache are threadsafe with uv generally...
             # but not on old Windows versions