refactor: update pruning strategy

[morph-dev]

What was wrong?

The pruning strategy of IdIndexedV1Store (deleting ~5% of db) was taking too long on large databases (example: 40sec on 10GB db).

How was it fixed?

After trying several approaches and measuring performance, I refactored the pruning logic:

1. Don't use triggers and update usage stats manually
   • Made delete queries return content_size to save few sql queries
2. Because of 1. no need for estimating how many entries to insert before pruning
   • This also allowed removing pruning_threshold from the config
3. Prune up to 5%, but no more than 100 items at the time

I run this version on one of Kolby's machines and metrics look ok to me.

For future PR-s:

• Use IdIndexedV1Store for history network
• Delete LegacyHistoryStore
• Delete triggers (might be useful in the future, but don't like to have unused code seating around)

To-Do

• [x] Clean up commit history and use conventional commits.