This gets the specs passing, and handles the fact that we expect
checkums to be pinned only to a particular source

This also avoids reading in .gem files during lockfile generation,
instead allowing us to query the source for each resolved gem to grab
the checksum

Finally, this opens up a route to having user-stored checksum databases,
similar to how other package managers do this!

Add checksums to dev lockfiles

Handle full name conflicts from different original_platforms when adding checksums to store from compact index

Specs passing on Bundler 3

https://github.com/rubygems/rubygems/commit/86c7084e1c