Scan checkpoint and resume — persists stage results to a local SQLite file.

Usage

let store = CheckpointStore::open("gossan-scan.db")?;
let scan_id = store.new_scan("example.com", &config_json)?;

// After each stage:
store.save_stage(scan_id, "subdomain", &targets, &findings)?;

// On resume:
let record = store.load(scan_id)?;
if let Some(stage) = record.stage("subdomain") {
    // skip subdomain scan, restore targets
}