feat: track space used by collection and builder

[tim-hm]

Problem

To implement subscription tiers, we need visibility into the amount of data stored. This requires tracking storage at both the collection and builder levels. The aggregate totals apply to both user-owned and builder-owned collections.

Proposed solution

1. Create a process (eg 5 min cron job) that aggregates the total storage used by a builder across all their collections.
2. Expose this information on the builder's profile, allowing them to monitor their usage against their subscription tier.

Acceptance Criteria

• The size of each collection is returned in the builder's profile.
• The implementation is efficient and does not introduce significant overhead to write operations (eg update periodically so its okay for the figure to drift slightly)