[cpackget] --concurrent-downloads (default 5) corrupts downloaded *.pdsc files

[thorstendb-ARM]

Describe the bug
When running "update-index -a" (where -a option skips already installed files, if an update is necessary, this is done in the next step) some files are not written into .Web folder. It seems they get downloaded to .Download, but the file move to .Web fails.

To Reproduce
Steps to reproduce the behavior:

1. Delete some (random) files from .Web folder
2. Run the cpackget with the following args: "update-index -a"
3. See some of the files are not copied

Expected behavior
All files that do exist in index.pidx but not in .Web folder should be added

Environment

• OS: windows 10

Additional context
Adding the option "-C 0" (disable concurrency) seems to solve the issue for "update-index -a", which means this can be related to concurrency in file operations

[thorstendb-ARM]

Wrote a new concurrent scheduler using semaphore. In the original version, one blocking download was done every n (concurrent) +1 downloads, but at least all files were spawned as thread (which resulted in much more threads than the concurrent number). There was no wait to finish spawned threads at the end of the loop, which caused the cut off or missing files.
The semaphore mechanism also allows that finished threads are immediately filled up with new threads instead of waiting for a bunch of threads to be finished before spawning the next.