Pruning

[megascatterbomb]

Changes:

• Allows a storage cap to be specified by the user, and deletes demos with no detections to stay within that limit on boot.
• Always deletes demos with no detections.
• Avoids deleting more than a certain % of demos in one go to mitigate catastrophic data losses (5% by default).
• Automatically cleans up hanging demos (demo blobs with no matching record in the database).

🔥 This PR has been tested in production 🔥

Example log output during boot: