Handle Connections and Protocol Selection with Known Contracts

[CyrusVorwald]

Since Clarity cannot dynamically dispatch to a contract based on a runtime value, use a fixed set of known connection contracts and handle protocol selection through predefined options.

• Define connection-trait
• Implement connection contracts for each protocol, conforming to the connection-trait.
• In the xCall implementation contract, maintain a list or mapping of known connection contracts.
• Admin should be able to add or remove connection contracts.
• The send-call function should be able to select and interact with connection contracts based on their identifier.