Use ty to type-check Python files (#17229)

I added mypy type‑checking in https://github.com/astral-sh/uv/pull/5332,
so I think it's a good time to switch to ty now :)

python/uv/_find_uv.py

@@ -94,7 +94,7 @@ def _user_scheme() -> str:
         user_scheme = sysconfig.get_preferred_scheme("user")
     elif os.name == "nt":
         user_scheme = "nt_user"
-    elif sys.platform == "darwin" and sys._framework:
+    elif sys.platform == "darwin" and sys._framework:  # ty: ignore[unresolved-attribute]
         user_scheme = "osx_framework_user"
     else:
         user_scheme = "posix_user"