* Add orphan pruning tests for Simplefin importer and implement pruning logic
- Introduced `SimplefinItem::ImporterOrphanPruneTest` to verify orphaned `SimplefinAccount` pruning scenarios.
- Added logic in `SimplefinItem::Importer` to remove orphaned `SimplefinAccounts` when upstream account IDs change.
- Ensured linked accounts via legacy FK or `AccountProvider` are preserved during pruning.
- Updated sync stats to track pruned accounts.
* Optimize SimplefinAccount query in importer to prevent N+1 issues
- Added eager-loading of `account` and `account_provider` associations when retrieving orphaned `SimplefinAccounts`.
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Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>
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