v0.3.3 — LangChain callback handler

Closes the framework coverage gap. Drop AegrailCallbackHandler() into your LangChain callbacks=[...] list and the active aegrail session gets pre-call budget checks, post-call token recording (OpenAI + Anthropic shapes including cache fields), tool_call audit events, and error events tagged with LangChain source. Chain lifecycle is intentionally noise-free. 8 new tests; battle-tested against the wheel. End of 0.3.x framework coverage arc: openai + anthropic + litellm SDKs auto-patched, LangChain via callbacks, every wrapper-of-the-above covered transparently.