feat(example): demonstrate V8 sandbox suspend and resume #4857

User Story

When validating OpenShell sandbox lifecycle through the V8 isolation-backend example, I need a simple JavaScript guest that I can suspend and resume from the OpenShell CLI and observe continuing from its retained state.

Description

Extract the V8 suspend/resume implementation and manual guest.js demonstration from #4765 into its own dependent PR. Keep the shared lifecycle APIs, gateway behavior, supervisor integration, and SDKs in the parent PR.

The example should retain a running JavaScript isolate across suspension, resume it under fresh runtime credentials, and preserve retained state when a restore launch fails. Document basic CLI commands in the example README.

Context

Depends on #4765 and its lifecycle contracts tracked by #4763. The operator requested and exercised this example while developing and validating suspend/resume.

Definition of Done

• The parent PR contains only the compatibility changes needed for the existing example to build with the new compute-driver contract.
• A dependent PR contains the V8 implementation, counter guest, example documentation, and focused tests.
• A CLI-driven suspend/resume run continues the same guest's count after a suspended interval and exits successfully.
• Failed restore launches leave retained state available for retry.