Avoid double resolution during source builds (#656)
## Summary
This PR ensures that we re-use the resolution to install the build
dependencies when building a source distribution. Currently, we only
pass along the list of requirements, and then use the `Finder` to map
each requirement to a distribution. But we already determine the correct
distribution when resolving!
Closes https://github.com/astral-sh/puffin/issues/655.
