Add sandbox container runtime v2

[ravenSanstete]

Summary

• Adds runtime_container v2 fields for workspace, lifecycle commands, network/env/mount/resource metadata.
• Adds runtime-owned per-trial workspaces, Docker container provider, and compose lifecycle command support.
• Wires phase admission through prepare/execute/score/finalize scheduler APIs and updates TerminalBench/IPI Coding Agent/AgentBench OS adapter metadata.
• Adds README badges, docs updates, and sandbox-coding-smoke example.

Tests

• python -m pytest tests/test_runtime_workspace.py tests/test_container_lifecycle.py tests/test_container_runtime_providers.py tests/test_resource_scheduler.py tests/test_agent_benchmark_adapters.py -q
• python -m pytest tests/test_runtime_workspace.py tests/test_container_lifecycle.py tests/test_container_runtime_providers.py tests/test_resource_scheduler.py tests/test_agent_benchmark_adapters.py tests/test_runtime_engine.py tests/test_runtime_controls_and_profiling.py -q
• python -m snowl.cli eval examples/sandbox-coding-smoke/project.yml --no-web
• python -m snowl.cli bench check terminalbench --adapter-arg dataset_path=
• python -m snowl.cli bench check ipi_coding_agent --adapter-arg dataset_path=
• python -m snowl.cli bench check agent_bench_os --adapter-arg dataset_path=
• python -m pytest -q