As part of the system-runner implementation, create pluggable backends for workload orchestration.

• taskset backend: Launch and manage processes with CPU affinity on bare metal.

• podman backend: Launch and manage standalone containers and pods using Podman CLI/API.

• kubeplay backend: Launch and manage pods/containers using podman kubeplay for YAML-driven deployments.

Each backend should provide a unified interface for scenario/config parsing, workload launch, and resource management, allowing system-runner to orchestrate experiments across all supported environments.