…ating downloads

Delay assignment of file_qty until it is known, but otherwise proceed to
initiating downloads

Since maxsize is dynamically computed as we go through the files.
The idea, I guess, was that it would grow rapidly before actual
downloads commense but it is not the case, so we endup with done%
being always close to 100% since we get those reports on final
downloads completed close to when individual files are downloaded.

So this should close #1407 .

But for total zarr file to be used, we needed to account also for
skipped files.  I added reporting of sizes for skipped files as well.
It seems there is no negative side effect on regular files download.
So now for the %done of zarr we might be getting to 100% of original
size having downloaded nothing.  But IMHO it is ok since user does
not care as much of how many "subparts" are downloaded, but rather
to have adequate progress report back.

There also could be side effects if  -e skip  and we skip
download of some updated files which would be smaller than the local
ones so altogether we would get over 100% total at the end.

… the modified code logic

Co-authored-by: John T. Wodder II <jwodder@users.noreply.github.com>