Properly include "data packages" in project

[jwodder]

There are several folders in dandi/ that contain data files but no Python source code, and we want these to be included when dandi is installed. Currently, these folders are automatically included by the combination of graft dandi in MANIFEST.in and include_package_data = True in setup.cfg, but because we set packages in setup.cfg to find: instead of find_namespace:, the folders themselves are not recognized by setuptools as packages. This combination of settings is deprecated, and the setuptools developers recommend using find_namespace: instead of find: for such situations.

[codecov]

Codecov Report

Merging #1029 (3f655c5) into master (6d8c31e) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1029      +/-   ##
==========================================
+ Coverage   87.64%   87.68%   +0.04%     
==========================================
  Files          65       65              
  Lines        8261     8261              
==========================================
+ Hits         7240     7244       +4     
+ Misses       1021     1017       -4     

Flag	Coverage Δ
unittests	87.68% <ø> (+0.04%)	⬆️

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Impacted Files	Coverage Δ
dandi/support/threaded_walk.py	92.85% <0.00%> (-1.79%)	⬇️
dandi/_version.py	45.96% <0.00%> (+1.75%)	⬆️

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[github-actions]

🚀 PR was released in 0.42.0 🚀