(VDB-68) Verify log block hash matches header block hash

- Delete header on conflict to prompt data refresh (cascade deletes all
  data associated with that block)
- Derive header hash from rpc payload rather than computing it from data
  (prevents hash mismatch between blockchain and cache)

pkg/transformers/vat_grab/repository.go

@@ -24,6 +24,13 @@ func (repository VatGrabRepository) Create(headerID int64, models []interface{})
 			tx.Rollback()
 			return fmt.Errorf("model of type %T, not %T", model, VatGrabModel{})
 		}
+
+		err = shared.ValidateHeaderConsistency(headerID, vatGrab.Raw, repository.db)
+		if err != nil {
+			tx.Rollback()
+			return err
+		}
+
 		_, err = tx.Exec(
 			`INSERT into maker.vat_grab (header_id, ilk, urn, v, w, dink, dart, log_idx, tx_idx, raw_log)
 	   VALUES($1, $2, $3, $4, $5, $6::NUMERIC, $7::NUMERIC, $8, $9, $10)`,