cleanup: remove dead code, fix bugs, refactor SSH dest parsing

- Remove debug printf calls from file.c
- Remove dead code: chunk_print, chunk_format, chunk_data_create/delete
- Remove unused config.use_single_send_per_file field
- Fix server_delete() no-op (double-pointer)
- Fix double cast (long)(long) -> ptrdiff_t in chunk.c
- Fix thread return value: thrd_error instead of 1
- Remove unused config param from receive_chunk_enqueue()
- Make queue_double_capacity() static
- Move SSH dest parsing into config.c as config_parse_ssh_dest()
- Fix test_config_ssh_dest to test parsing round-trip
- Remove chunk_format test (obsolete format)
- Replace chunk_data_delete with data_destroy in tests

src/shared/socket.h

@@ -15,7 +15,7 @@ typedef struct Server {
 
 Server *server_create(int port);
 void server_listen(Server *server, void (*handler)(int file_descriptor));
-void server_delete(Server *server);
+void server_delete(Server **server);
 
 typedef struct Client {
   struct sockaddr_in address;