service: add ark-network/ark

[tiero]

Add Ark and improve testing

What's Changed

🎯 Add Ark

• Added Ark as default Bitcoin layer two solution
• New commands: nigiri ark and nigiri arkd for wallet management
• Updated docs with Ark usage examples and initialization steps

🧪 Better Testing

• Introduced Docker client interface and mock implementation
• No more Docker-in-Docker testing headaches
• Consolidated Docker code for better maintainability

🔧 Code Cleanup

• Organized commands in logical groups (Core, Bitcoin/Elements, Ark, Lightning)
• Better service endpoints logging
• Unified YAML parsing and error handling

Try it out!

Start with Ark enabled

$ nigiri start --ark

Initialize Ark wallet

$ nigiri ark init --network regtest --password secret --server-url localhost:7070

[tiero]

Are these good for dev? @altafan