can no append to existing slices

[muir]

allow appending to existing slices

[codecov-commenter]

Codecov Report

Merging #6 (4b78c09) into main (576e86b) will increase coverage by 0.62%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   79.37%   80.00%   +0.62%     
==========================================
  Files           3        3              
  Lines         223      230       +7     
==========================================
+ Hits          177      184       +7     
  Misses         29       29              
  Partials       17       17              

Impacted Files	Coverage Δ
unpack.go	73.10% <100.00%> (+1.68%)	⬆️

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