Description

This is a follow-up to #8130, where the rethdb receipts fetcher was encapsulated in its own type RethDBReceiptsFetcher. This allows us now to persist a database instance/handle. The instance would replace the dbPath string field. It still needs to be determined how to persist the instance, since the rethdb fetcher currently opens the database on the fly on every request, and then throws away the db instance. We probably need to create a function rdb_open_db that returns a pointer to the instance as an unsafe Go pointer or so. And rdb_read_receipts would then receive this pointer instead of the db path string.

Testing

Existing tests should be adapted and extended where appropriate.