feat: support Alibaba Function Compute as sandbox runtime provider

## Background

ROCK currently supports multiple deployment modes including Docker, Ray, and K8s. Adding Alibaba Cloud Function Compute (FC3) as a sandbox runtime provider would enable serverless deployment of ROCK sandboxes, reducing operational overhead and enabling auto-scaling.

## Feature Request

Add comprehensive support for Alibaba Cloud Function Compute 3.0 (FC3) as a sandbox runtime provider with three deployment modes:

1. **Custom Runtime**: Lightweight Python runtime with bootstrap script
2. **Custom Container**: Full Docker container deployment
3. **Hybrid Adapter**: HTTP/WebSocket adapter for FC3 function integration

## Key Components

### FC3 Client
- `FC3Sandbox`: Main sandbox client with session management
- `CircuitBreaker`: Thread-safe fault tolerance with OPEN/CLOSED/HALF_OPEN states
- WebSocket reconnection with exponential backoff retry
- Custom exceptions for error handling

### FC3 Rocklet
- `runtime/`: Custom Runtime bootstrap and configuration
- `container/`: Custom Container Dockerfile and configuration
- `adapter/`: Hybrid Adapter HTTP/WebSocket server with path traversal protection

### Tests
- 126 test cases covering client, adapter, and runtime configurations

## Benefits

- **Serverless**: No infrastructure management required
- **Auto-scaling**: Automatic scaling based on workload
- **Cost-effective**: Pay-per-use pricing model
- **High availability**: Built-in fault tolerance

Start by locating the existing sandbox runtime providers, then compare their structure with the proposed runtime/, container/, and adapter/ components. Review the FC3 client, session management, circuit breaker, WebSocket retry, and path-traversal requirements before running or adding the stated 126 tests. Done means all three FC3 deployment modes and their listed safeguards are supported.

Written by the indexing model from the issue text.