Implement FuzzNode and FuzzChain classes for multi-step attack chains
with pipe operator syntax, inspired by FuzzyAI architecture.
- FuzzNode: Single LLM call with {var} template substitution
- FuzzChain: Sequential execution passing output as input
- Pipe operator (|) for composing nodes into chains
- LLMProvider protocol for provider abstraction
- 22 unit tests covering composition and execution