ADOGitClient class download_zip method not displaying progress bar

I believe this is due to the server in question responding without a content-length header because of chunked encoding.

I initially found your project in a roundabout way because of a similar issue with azure-devops-python-api where when pulling a tree zip, a Generator would be created, so there was no reasonable way to get a progress update bar going. The interface you've created is a lot simpler and easy to use, which is perfect for my purposes, and has made my development much more streamlined, but it would be nice to find a way to show a progress bar. For large mono-repos, a download can take quite some time.

Perhaps there is a way to recursively get all items from a tree via a given path and then calculate an approximate total size? I played a bit with hacking up download_zip to simply get all tree entries from a given path, ignoring content and grabbing metadata, and it did seem to have sizes returned. Perhaps if we summed these, we could simply pass them into the download_zip call and have that be the fall back if the content-length isn't provided?

Start at the ADOGitClient.download_zip entry point and inspect how responses without a content-length header are handled. Review the proposed tree-entry metadata approach and its effect on progress reporting; done means large downloads show a useful progress bar even when the server uses chunked encoding. The issue names no file or test path.