Fix Claims pallet

[shekohex]

The original claims pallet from Polkadot only supported one type of accounts, ecdsa accounts or the one used in EVM/Eth.
We found the following issue with our implementation:

• the way we encode the MultiAddress is messed up due to SCALE encoing https://github.com/webb-tools/tangle/blob/541ae696acc18a5a8c983be5e84943f7a747141c/pallets/claims/src/lib.rs#L327
• while working with substrate accounts, polkadot.js wraps the bytes to be signed in a <Bytes> and </Bytes> tags.