refactor(sandboxer): redesign container bootstrapping

[dungdm93]

Objective

Enable job and service container execution across sandboxer engines (docker, host, and incus) with a unified, resilient bootstrapping lifecycle.

High-Level Design

• Unified Bootstrapping (container.Bootstrap): Replaces the stateful bootstrapper interface with a functional pipeline handling network coordination, parallel service provisioning, and automatic rollback on failure.
• Engine Ownership & Lazy Initialization:
  • Docker Engine: Directly manages its job container lifecycle while delegating auxiliary services to the shared bootstrapper.
  • Host & Incus Engines: Lazily initialize container runtimes only when container workloads are requested, keeping containerless sandboxes lightweight.
• Lifecycle Integration: Registers cleanup hooks on the sandbox lifecycle to guarantee reliable teardown of networks and containers upon termination.