Used Contracts

[peterjan]

This PR updates the upload manager to return a set of used contracts. This avoids looping the sectors after calling upload/migrate and build it manually, but it also makes sure the contracts contain potential renewals.

[peterjan]

Was going to add a commit that improves fetchUsedContracts but I see you are doing something similar in #602 so I'll wait for that. I would personally do both, but I agree that it's mostly useful in fetchUsedContracts so we might be able to drop this in favour of #602 . It's more correct though to do it in both the uploader and the bus I think 🤔

edit: added it anyway, was almost done and took diff. approach

[ChrisSchinnerl]

Wait why is that? Can't you directly pass used to UpdateSlab instead of looping over slab.Shards again?

[peterjan]

no you can't because it'll only contain the used contracts for the migrated shards, I updated the code though so migrateSlab takes care of that for you

[ChrisSchinnerl]

Ok in that case can we rename Migrate to UploadShards? It was quite confusing to me that in one place we call Migrate and are able to return used without modification and in another we call migrateSlabs and we still have to merge the maps.
Only to realise that Migrate isn't actually migrating but only uploading.