[Feature Request] Add sandbox resource usage metrics and limits

[rehan243]

Feature Description

Expose real-time resource usage (CPU, memory, disk) for running sandboxes and allow configurable limits.

Use Case

When using E2B for AI code execution in production:

1. Need to prevent runaway processes from consuming resources
2. Want to track resource usage for billing/optimization
3. Need to set per-sandbox memory limits for multi-tenant environments

Proposed API

sandbox = Sandbox(memory_limit_mb=512, cpu_limit=1.0)
metrics = sandbox.get_metrics()  # {cpu_pct: 45, mem_mb: 200, disk_mb: 50}

This would make E2B more suitable for production deployments with strict resource governance. Great platform!

[linear]

ENG-3755