Callback server wrapper

[Xiangs18]

This PR updates and relocates the original workspace_downloader_helper.py file

1. updated/tested the workspace_downloader.py script
2. Will update workspace_uploader.py in RE2022-217: Workspace uploader performance #426

[codecov]

Codecov Report

Attention: 25 lines in your changes are missing coverage. Please review.

Comparison is base (170017a) 46.90% compared to head (1a8fc2c) 46.83%.

Files	Patch %	Lines
src/loaders/common/callback_server_wrapper.py	0.00%	19 Missing ⚠️
...aders/workspace_downloader/workspace_downloader.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #554      +/-   ##
==========================================
- Coverage   46.90%   46.83%   -0.08%     
==========================================
  Files          73       73              
  Lines        6306     6318      +12     
==========================================
+ Hits         2958     2959       +1     
- Misses       3348     3359      +11     

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[MrCreosote]

So this PR was just supposed to be rename & relocate - no changes. The changes should show up in the other PR where they're part of the set of changes to support the new assemblyutil parallelization