Add type annotations

[oliverchang]

[github-actions]

This issue has not had any activity for 60 days and will be automatically closed in two weeks

See https://github.com/google/osv.dev/blob/master/CONTRIBUTING.md for how to contribute a PR if you're interested in helping out.

[github-actions]

This issue has not had any activity for 60 days and will be automatically closed in two weeks

See https://github.com/google/osv.dev/blob/master/CONTRIBUTING.md for how to contribute a PR if you're interested in helping out.