Fuzz charon with malicious charon node

[dB2510]

🎯 Problem to be solved

Currently we have simnet beacon mock fuzz which acts as a beacon node fuzzer by returning random responses for all the beacon node API calls.
As part of our fuzz testing efforts for charon, we need to implement a malicious charon node which should act as a charon fuzzer in a cluster. The malicious charon node should send random responses to its peers in a cluster over defined libp2p protocols.

🛠️ Proposed solution

• Add charon_peer_fuzz feature flag to enable charon peer fuzzing over p2p network in a cluster via CLI.
• Wrap existing p2p default writers in sendRecvOpts.writersByProtocol to write random messages when called by send functions in p2p/fuzz.go as something like:

type fuzzWriter struct {
	w pbio.Writer
}

func (fw *fuzzWriter) WriteMsg(msg proto.Message) error {
	cloneMsg := proto.Clone(msg)
	fuzz.New().Fuzz(cloneMsg)

	return fw.w.WriteMsg(cloneMsg)
}

• Add an SendRecvOption function as:

func WithFuzzWriter() func(*sendRecvOpts) {
	return func(opts *sendRecvOpts) {
		for pID := range opts.writersByProtocol {
			opts.writersByProtocol[pID] = func(s network.Stream) pbio.Writer {
				return &fuzzWriter{w: pbio.NewDelimitedWriter(s)}
			}
		}
	}
}

• Use WithFuzzWriter when charon_peer_fuzz feature flag is enabled.

🧪 Tests

• Tested by new automated compose tests
• Manually tested on core team/canary/test clusters
• Manually tested on local compose simnet