eg/870-add-circuit-relay-dcutr-autonat-demonstration

[Winter-Soren]

What was wrong?

Demonstrating an example of NAT traversal using Circuit Relay v2, DCUtR hole punching, and AutoNAT was missing from the codebase.

Issue #870

How was it fixed?

Implemented a comprehensive NAT traversal example that demonstrates the complete flow:

1. A publicly reachable relay node running Circuit Relay v2
2. A listener node behind NAT that advertises via relay and supports DCUtR
3. A dialer node that connects via relay and upgrades to direct connection via hole punching

The implementation includes three components:

• relay.py: Publicly accessible relay node with resource management
• listener.py: NAT'd peer that accepts connections via relay and supports direct upgrades
• dialer.py: NAT'd peer that connects through relay and attempts hole punching

graph TD
    subgraph "Dialer (Behind NAT)"
        A[Dialer Node]
        A1[AutoNAT]
        A2[Circuit Relay CLIENT Role]
        A3[DCUtR Protocol]
    end
    
    subgraph "Public Relay"
        B[Relay Node]
        B1[Circuit Relay HOP Role]
        B2[Resource Management]
    end
    
    subgraph "Listener (Behind NAT)"
        C[Listener Node]
        C1[AutoNAT]
        C2[Circuit Relay STOP Role]
        C3[DCUtR Protocol]
    end
    
    A -->|"1. Connect via relay"| B
    B -->|"2. Relay connection"| C
    A -->|"3. DCUtR hole punching"| C
    
    %% Component connections
    A --- A1
    A --- A2
    A --- A3
    B --- B1
    B --- B2
    C --- C1
    C --- C2
    C --- C3
    
    class A,C natNode
    class B publicNode

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To-Do

• Clean up commit history
• Add or update documentation related to these changes
• Add entry to the release notes

[seetadev]

@Winter-Soren : Appreciate your great efforts, Soham.

Re-ran the CI/CD pipeline. There are a couple of issues, which need resolution.

We will need a proper screencast demonstrating the example along with proper documentation to enable hole punching interop testing as the next step.

CCing @acul71, who could help you on the hole punching interop testing front using the example as a starting point.