We now show the fully-resolved URL, rather than the URL as given by the
user, _everywhere_ except for the output resolution file (which should
retain relative paths, unexpanded environment variables, etc.).
Closes https://github.com/astral-sh/puffin/issues/687.
This PR adds caching support for built wheels in the installer.
Specifically, the `RegistryWheelIndex` now indexes both downloaded and
built wheels (from registries), and we have a new `BuiltWheelIndex` that
takes a subdirectory and returns the "best-matching" compatible wheel.
Closes#570.
Zanie Blue