Remove PoR parameters, add merkle root for storage proofs

[markspanbroek]

Update Request to accomodate new proving scheme:

• Remove PoR parameters
• Remove total number of chunks
• Add merkle root of the dataset

[markspanbroek]

Rationale for removing "total number of chunks" from the request:

1. We don't need it to download the slot data. The cid points to the manifest, and the manifest provides enough information to determine which range of blocks to download for a given slot index.
2. We don't need it for the SNARK proofs, because it only needs to know how many shards there are in a slot, and it can calculate that from the slot size (already on chain) and the shard size (fixed in the SNARK)

[AuHau]

Is this related to https://github.com/codex-storage/nim-codex/issues/579 ?

[markspanbroek]

Is this related to codex-storage/nim-codex#579 ?

Yes, this is part of it.