## Summary
This PR adds support for `prepare_metadata_for_build_wheel`, which
allows us to determine source distribution metadata without building the
source distribution. This represents an optimization for the resolver,
as we can skip the expensive build phase for build backends that support
it.
For reference, `prepare_metadata_for_build_wheel` seems to be supported
by:
- `hatchling` (as of
[1.0.9](https://hatch.pypa.io/latest/history/hatchling/#hatchling-v1.9.0)).
- `flit`
- `setuptools`
In fact, it seems to work for every backend _except_ those using legacy
`setup.py`.
Closes#599.
Charlie Marsh
e26dc8e33d