[CHECKLIST] Claims pallet updates for launch

[drewstone]

Overview

Current claims pallet from the Polkadot launch is built around ECDSA signatures/Ethereum addresses. A claim is claimed by signing a string with your Ethereum address.

We need to expand this to support also Substrate claims. We need to also modify the functionality so that claims are time-limited, if they aren't claimed within a certain block interval (say [0, 1000000]) then the claim is invalidated and all remaining tokens go to the chain treasury.

The general feature set we want to support will be

• Support for ECDSA and Substrate claims
• Claim to an address of their choosing (i.e on Substrate or on the EVM).
• Time-sensitive claims
• Ability to reclaim funds from unclaimed expired claims
• Ability to create new claims (for future airdrops/phases, etc.)

Checklist

• Add support for creating claims for Substrate addresses (we don't need to require signature, should just be extrinsic based)
• Add time-sensitive nature of a given claim
• Add extrinsic to send unclaimed funds to treasury (support submitting a batch of unclaimed expired claims)
• Add tests