Reveal size, mtime of all files in a folder

[meejah]

fixes #476

[codecov]

Codecov Report

Merging #478 (d779057) into main (165a553) will increase coverage by 3.47%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #478      +/-   ##
==========================================
+ Coverage   87.98%   91.46%   +3.47%     
==========================================
  Files          35       35              
  Lines        2955     2963       +8     
  Branches      339      339              
==========================================
+ Hits         2600     2710     +110     
+ Misses        280      181      -99     
+ Partials       75       72       -3     

Flag	Coverage Δ
integration	70.50% <37.50%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/magic_folder/config.py	97.77% <100.00%> (+0.26%)	⬆️
src/magic_folder/web.py	98.23% <100.00%> (+0.03%)	⬆️
src/magic_folder/downloader.py	96.06% <0.00%> (+0.43%)	⬆️
src/magic_folder/uploader.py	95.94% <0.00%> (+0.67%)	⬆️
src/magic_folder/snapshot.py	95.48% <0.00%> (+1.12%)	⬆️
src/magic_folder/client.py	96.47% <0.00%> (+1.17%)	⬆️
src/magic_folder/api_cli.py	90.55% <0.00%> (+3.33%)	⬆️
src/magic_folder/cli.py	68.59% <0.00%> (+9.74%)	⬆️
src/magic_folder/util/eliotutil.py	89.18% <0.00%> (+14.18%)	⬆️
... and 3 more

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[tomprince]

This looks good once get_all_current_snapshot_pathstates is changed to return a list or dict. I agree that it would be better to avoid allocating one, but I can't think of an easy to do so without providing a footgun re: transactions here.