Add langchanin callback handler

agentops/integration/callbacks/langchain/README.md

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+# AgentOps LangChain Callback Handler
+
+This callback handler enables seamless integration between LangChain and AgentOps for tracing and monitoring LLM applications.
+
+## Features
+
+- **Complete Coverage**: Supports all LangChain callback methods 
+- **Session Tracking**: Creates a session span that serves as the root for all operations
+- **Proper Hierarchy**: Maintains parent-child relationships between operations
+- **Complete Instrumentation**: Tracks LLMs, chains, tools, and agent actions
+- **Error Tracking**: Records errors from LLMs, chains, and tools
+- **Streaming Support**: Handles token streaming for real-time insights
+- **Attribute Capture**: Records inputs, outputs, and metadata for all operations
+- **Error Resilience**: Handles errors gracefully to ensure spans are always properly closed
+
+## Supported Callbacks
+
+The handler implements all LangChain callback methods:
+
+| Method | Description | Span Kind | Attributes |
+|--------|-------------|-----------|------------|
+| `on_llm_start` | Start of an LLM call | `llm` | Model, prompts, parameters |
+| `on_llm_end` | End of an LLM call | `llm` | Completions, token usage |
+| `on_llm_new_token` | Streaming token received | N/A | Token count, last token |
+| `on_llm_error` | LLM call error | `llm` | Error details |
+| `on_chat_model_start` | Start of a chat model call | `llm` | Model, messages, parameters |
+| `on_chain_start` | Start of a chain | `task` | Chain type, inputs |
+| `on_chain_end` | End of a chain | `task` | Outputs |
+| `on_chain_error` | Chain execution error | `task` | Error details |
+| `on_tool_start` | Start of a tool call | `tool` | Tool name, input |
+| `on_tool_end` | End of a tool call | `tool` | Output |
+| `on_tool_error` | Tool execution error | `tool` | Error details |
+| `on_agent_action` | Agent taking an action | `agent` | Tool, input, log |
+| `on_agent_finish` | Agent completing a task | `agent` | Output, log |
+| `on_text` | Arbitrary text event | `text` | Text content |
+
+All spans have appropriate attributes such as:
+- Model information for LLM spans
+- Input/output for all operations
+- Tool names and types
+- Chain types and configurations
+- Error details for failed operations
+
+## Troubleshooting
+
+If you're not seeing data in AgentOps:
+
+1. Check that your API key is correctly configured
+2. Ensure you're passing the handler to all relevant components
+3. Verify that all operations are properly ending/closing
+
+## How It Works
+
+The callback handler:
+1. Creates a session span when initialized
+2. Intercepts LangChain callbacks for various operations
+3. Creates appropriate spans with meaningful attributes
+4. Maintains proper parent-child relationships
+5. Automatically cleans up and ends spans when operations complete 

agentops/integration/callbacks/langchain/__init__.py

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+"""
+LangChain integration for AgentOps.
+
+This module provides the AgentOps LangChain integration, including callbacks and utilities.
+"""
+
+from agentops.integration.callbacks.langchain.callback import (
+    LangchainCallbackHandler,
+    AsyncLangchainCallbackHandler,
+)
+
+__all__ = [
+    "LangchainCallbackHandler",
+    "AsyncLangchainCallbackHandler",
+]