persist method
Persists the artifact to disk and returns the absolute path.
Implementation
Future<String> persist({String runsRoot = '.spectra/runs'}) async {
final dir = Directory(p.join(runsRoot, runId));
dir.createSync(recursive: true);
final file = File(p.join(dir.path, 'proof.md'));
file.writeAsStringSync(toMarkdown());
return file.path;
}