Bug in `ArchivalState::get_addition_record_indices_for_block`

This function returns a `Option<HashMap<AdditionRecord, Option<u64>>>` to enumerate all addition records (transaction outputs) in a block. But it fails to take into account that the same addition record can be present in a block multiple times. So the return type might have to be changed to `Option<HashMap<AdditionRecord, Option<Vec<u64>>>>`.