Torrent based multi-file transfer unfinished

During the integration testing, the bookkeeper reported unfinished transfers for multiple-file transfers.

***** Bookkeeper localhostsnbbookkeeper localhost:5000 informations display *****
Connected clients :
	* Session localhostsnbclient0_sestransfer0 is active
		 - output_localhosteth0_0.out	159386400 bytes	from 10.73.136.79:5001	UPLOADING	105%	-Bi/s	06-10-2023 09:59:24	2935ms	N/A		
		 - output_localhosteth0_1.out	159386400 bytes	from 10.73.136.79:5001	UPLOADING	105%	-Bi/s	06-10-2023 09:59:27	606ms	N/A		
		 - output_localhosteth0_2.out	159386400 bytes	from 10.73.136.79:5001	UPLOADING	105%	-Bi/s	06-10-2023 09:59:24	3540ms	N/A		
	* Session localhostsnbclient1_sestransfer0 is active
		 - output_localhosteth0_0.out	159386400 bytes	from 10.73.136.79:5001	FINISHED	100%	-Bi/s	N/A	0ms	06-10-2023 09:59:25		
		 - output_localhosteth0_1.out	159386400 bytes	from 10.73.136.79:5001	DOWNLOADING	0%	-Bi/s	06-10-2023 09:59:25	1822ms	N/A		
		 - output_localhosteth0_2.out	159386400 bytes	from 10.73.136.79:5001	DOWNLOADING	0%	-Bi/s	06-10-2023 09:59:25	1720ms	N/A

On the other hand, the seed client correctly reports that every file was successfully uploaded once.
Data files are also present on the destination client. but without the resume torrent file:

total 458M
   0 drwxr-xr-x 3 rsipos np-comp   23 Oct  6 09:59 ..
153M -rw-r--r-- 1 rsipos np-comp 153M Oct  6 09:59 output_localhosteth0_0.out
348K -rw-r--r-- 1 rsipos np-comp 347K Oct  6 09:59 .resume_file_output_localhosteth0_0.out
928K -rw-r--r-- 1 rsipos np-comp 925K Oct  6 09:59 bittorrent.log
153M -rw-r--r-- 1 rsipos np-comp 153M Oct  6 09:59 output_localhosteth0_1.out
   0 drwxr-xr-x 2 rsipos np-comp  177 Oct  6 09:59 .
153M -rw-r--r-- 1 rsipos np-comp 153M Oct  6 09:59 output_localhosteth0_2.out

This seems to indicate a problem how the downloader/leach client is finishing and reporting the transfers in case the transfer consists of multiple files.

Start with the integration-test scenario described in the issue and trace the downloader/leech client handling of multi-file transfers. Compare the bookkeeper status with the seed client’s report and the destination files, including the missing resume torrent file. Done means every file is correctly finalized and reported as finished for the destination client.