feat: brc21 proof of concept

[nud3l]

Description

Adds a BRC21 proof of concept implementation. BRC21 are tokens that can be transferred on Bitcoin similar to BRC20 but that are originating on another chain.

The POC implements:

• Inscribe minting INTR onto Bitcoin regtest
• Parse the minting inscription in a smart contract and verify the Bitcoin transaction inclusion via the Interlay BTC relay
• Inscribe the burning of INTR onto Bitcoin regtest
• Parse the redeeming inscription in a smart contract and verify the Bitcoin transaction inclusion via the Interlay BTC relay

Reference: https://interlay-labs.gitbook.io/brc-21/

Changes

• Adds access to the BTC relay via the contracts pallet
• Adds support for rust-bitcoin types within the bitcoin crate
• Adds the BRC21 proof of concept

Checklist

N/A

[nud3l]

Moved the contract and docs to https://github.com/bob-collective/bob