Avoid enforcing incorrect hash in mixed-hash settings (#17157)
## Summary
Right now, when we return a `Dist` from a lockfile, we concatenate all
hashes for all distributions for a given package. In the case of
https://github.com/astral-sh/uv/issues/17143, I think that means we'll
return the SHA256 from the sdist, plus the SHA512 from the wheel. If the
wheel was previously installed (i.e., it's in the cache), and we
computed the SHA256 at that point in time, then `Hashed::has_digests`
would return `true` because we have _at least_ one SHA256. We now limit
the hashes to the distribution that we expect to install.
Closes https://github.com/astral-sh/uv/issues/17143.
