[WIP] Update binary signature validation logic

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Our rule for checking if a binary has an expired signature currently looks for if the binary was signed by a certificate which is currently expired. However, I think this logically doesn't make sense - the signature is valid as long as the binary was signed during the certificates validity period, but it doesn't become unsafe because the certifiacate can no longer sign new things. Double check that we are correctly collecting all the needed fields to change this logic, add new data collection if required, and then update the rule logic to check that the certificate that was used for signing was in its validity period at the time the signature was made, instead of just checking if the signature is now expired.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.