Retrieve completed challenges gracefully for UI

Currently the challenges view of the provider UI uses a hack to render the completed ones by storing the ones that were seen by the page in its localStorage and consulting it on reloads. However, using the front end this way shifts responsibility and hides that the chain is the actual source of truth, so it's better to come up with an alternative way of doing that (and avoiding the clunk with things crashing upon schema changes etc).

I'd rather steer away from having schema hand encoded via some rehydration. Or if we really want to land it, we should probably enforce the schema with versions via something like zod so there's less chance to experience drift when anything challenge-related moves sideways and this snippet is forgotten.

And while we're on this, let's talk about the role of local storage in UI overall: if I remember correctly, it was introduced to keep challenges that have already expired visible to the provider in UI. But it should not become a source of truth that we rely on, only a cache in the best case. And what would make most sense is probably reconstructing the resolved challenges via querying some block range on chain for respective events, or just straight out abandoning this functionality and only leaving unresolved ones visible as it's ultimately the way it's meant to be.

Originally posted by @ilchu in https://github.com/paritytech/web3-storage/pull/194#pullrequestreview-4505275989

Start with the provider UI's challenges view and trace how completed challenges are stored in and restored from localStorage. Review the surrounding challenge data flow and determine whether resolved challenges should be reconstructed from chain events or omitted; the issue is done only after a source-of-truth decision and an agreed implementation are established.