engine: per-state and machine meta

[fruwe]

Summary

• Sync the bundled machine schema to accept top-level and per-state meta objects.
• Expose machine-level meta on Machine and state-level meta on State.
• Cover that meta validates and is visible to hosts, while remaining absent from snapshots and ignored by dispatch.

Closes #47

Validation

• .venv/bin/ruff check .
• .venv/bin/mypy src
• .venv/bin/python -m pytest -q
• HAREL_SPEC_DIR=/Users/chris/src/personal/harel HAREL_CONFORMANCE_DIR=/Users/chris/src/personal/harel-conformance .venv/bin/python -m pytest conformance -q