Use dir metadata for top hash

[sir-sigurd]

TODO

• [x] Unit Tests

[codecov-commenter]

Codecov Report

Merging #1647 into master will increase coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1647      +/-   ##
==========================================
+ Coverage   85.04%   85.05%   +0.01%     
==========================================
  Files          31       31              
  Lines        4207     4210       +3     
==========================================
+ Hits         3578     3581       +3     
  Misses        629      629              

Impacted Files	Coverage Δ
tests/integration/test_packages.py	100.00% <0.00%> (ø)
quilt3/packages.py	90.59% <0.00%> (+0.01%)	:arrow_up:

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[akarve]

Per discussion we should merge this as part for quilt3 4.x so as not to merge a potentially breaking change into 3.x.