Implement go-libp2p interop tests (echo protocol)

Summary

Implement interop tests between py-libp2p and go-libp2p using the echo protocol, following the existing pattern from nim-libp2p interop tests.

Motivation

• Interop testing ensures py-libp2p works correctly with other libp2p implementations
• go-libp2p is the reference implementation, making this high-value testing
• The framework already exists (nim interop), just needs to be extended for Go
• Improves confidence in py-libp2p's cross-implementation compatibility

Current State

tests/interop/go_libp2p/test_go_basic.py contains only a placeholder test:

def test_go_libp2p_placeholder():
    assert True, "Placeholder test for go-libp2p interop tests"

No actual interop testing is performed.

Proposed Implementation

Following the nim-libp2p structure, create:

tests/interop/go_libp2p/
conftest.py # Pytest fixtures to build/start Go server
go_echo_server.go # Simple Go echo server using go-libp2p
test_echo_interop.py # Python tests connecting to Go server
scripts/
setup_go_echo.sh # Build script for Go binary

Test Flow

1. Build step - Build script compiles the Go echo server binary

2. Test setup - Pytest fixture starts the Go server as a subprocess

3. Interop test - Python test uses py-libp2p to connect and test the echo protocol

4. Teardown - Server is stopped after tests complete

References

• Go libp2p echo example:
  https://github.com/libp2p/go-libp2p/tree/master/examples/echo

• Existing nim-libp2p interop:
  nim_libp2p

Are you planning to do it yourself in a pull request?

Yes

Start by comparing tests/interop/nim_libp2p with the placeholder in tests/interop/go_libp2p/test_go_basic.py, then review the referenced go-libp2p echo example. Add the named Go server, pytest fixtures, echo interop tests, and setup script so the server builds, the Python client exchanges echo messages, and teardown completes cleanly.