fix: Remove created_at filtering (M2-9658)

[andrevitalb]

📝 Description

🔗 Jira Ticket M2-9658

This PR removes the created_at filtering from the existing answers check when submitting answers. This specific filtering was causing issues when submitting answers locally through the mobile app due to this check relying on exact timestamp matching, which wasn't allowing for answers to be submitted.

Since we are already filtering by applet_id, activity_id and submit_id, the desired behavior will still be maintained.

Some potential edge cases were evaluated:

1. Resubmission attempts: If a user attempts to submit an answer multiple times (could be due to network issues), the submit_id should remain consistent across attempts, so we’d still be catching those.

2. Multiple submissions for same activity: If a user has multiple submissions for the same activity, each of those will have a different submit_id.

Since we’d still check for submit_id (which is unique), we can be confident that this check is sufficient for uniquely identifying submissions.

🪤 Peer Testing

In order to test these specific changes, submitting any activity via both the web and mobile app should succeed without issues (no "Unstable internet connection" on mobile).

📝 Notes

Extra cleanup work will be needed to remove the actual created_at parameter from the input schema (AnswersCheck) once the mobile app PR has been merged

[github-actions]

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[jodybrookover]

Can someone confirm this will continue to work for old mobile clients since we can't guarantee all users will ever update.