[Enhancement] Speed up advisory sync ingestion for growing OSV datasets

[sonukapoor]

Summary

Improve local advisory DB sync performance by reducing SQLite write overhead during OSV dump ingestion.

Closes #78.

What Changed

• reuse prepared SQLite statements across the advisory DB lifecycle
• add a bulk advisory upsert path that writes all parsed advisories in a single outer transaction
• parse OSV advisories first, then perform one coordinated DB write pass instead of one transactional upsert per record

Benchmark

Local benchmark on the same machine using the same command and OSV npm dump:

• before: 87.53s real
• after: 8.84s real
• improvement: about 9.9x faster end-to-end

Command used:

authoritative
/usr/bin/time -p node dist/index.js advisories sync --output /tmp/advisories.db

Verification

• npm test
• npm run build