Sandbox metrics include disk and network

GET /v1/sandboxes/{id}/metrics and sbx.metrics() now return diskUsedBytes (bytes used on the root file system), diskReadBytesPerSecond, diskWriteBytesPerSecond, diskReadOpsPerSecond, diskWriteOpsPerSecond, networkReceivedBytesPerSecond and networkSentBytesPerSecond for each point and for latest. Disk figures are counted by the sandbox's own kernel; network figures by the host, for every connection the sandbox opens and every request it serves. A value that was not measured is null, never zero. The sandbox's Activity tab charts disk used, disk reads and writes, and network in and out; runtime sandboxes metrics prints them; the Python, Go and TypeScript SDKs return them; and getMetrics() in withruntime/e2b now returns diskUsed. OpenTelemetry exports send them as runtime.sandbox.disk.usage, runtime.sandbox.disk.limit, runtime.sandbox.disk.io, runtime.sandbox.disk.operations and runtime.sandbox.network.io (metrics).