Add Discrete Log Contract Primitives

[MatthewLM]

Discrete Log Contract primitives shall be added according to the general design outlined here: https://talk.peercoin.net/t/atomic-dlcs-with-distributed-oracles/16641

The following tasks need to be completed:

• Move to a library such as secp256k1-zkp that supports adaptor signatures with MuSig2.
• Ensure new library is working on Windows: Test Windows library changes #37
• Wire underlying MuSig2 functions and create MuSig2 abstraction with adaptor support.
• Write class to specify DLC contract terms. DLCs should use a versioned protocol to allow future upgrades.
• Write class for handling DLC state with serialisation so DLC data can be shared between counterparties.
• Create MuSig2 key for funding DLC.
• Create Taproot MAST structure with APO path.
• Add CET (Contract Execution Transaction) using adaptor signatures.
• Add RT (Refund Transaction).
• Add FT (Funding Transaction).
• Allow key-path settlement. (Maybe in a future version)
• CET completion via adaptor-signature decryption.
• Unit testing
• Testnet example