target: Add libbitcoin-server fuzzing support

[str8outtaheap]

Summary

Adds support for fuzzing libbitcoin-server (bs) as a fuzzing target. libbitcoin-server (compared to libbitcoin-node) includes a ZeroMQ query interface with address indexing, allowing us to query blockchain state, transactions, and addresses. This provides better control and introspection capabilities (might be heavier/slower).

What's included

• LibbitcoinTarget: Spawns and manages libbitcoin-server process
• LibbitcoinGenericScenario: P2P fuzzing scenario with inbound-only connections
• Dockerfile.libbitcoin: Builds bs at /opt/libbitcoin/bin/bs with AFL++ instrumentation
• scripts/test-libbitcoin.sh: Manual verification of server startup

Notes / Limitations

• Uses native libbitcoin consensus (not libconsensus wrapper)
• Inbound connections only (libbitcoin-server does not support dynamic peer management)
• No mocktime support (libbitcoin-server does not support mocktime)

Testing

# Build Docker image
docker build -f Dockerfile.libbitcoin -t fuzzamoto-libbitcoin .

# Run container
docker run -it -v $(pwd):/fuzzamoto fuzzamoto-libbitcoin bash

# Inside container:
/fuzzamoto/scripts/test-libbitcoin.sh
cargo test --release --package fuzzamoto -- libbitcoin --ignored

WIP

• Nyx VM integration
• ZeroMQ support for HasTipHash/HasTxOutSetInfo oracles
• Seed corpus generation