fix(narugo): fix metadata reading for png format, raise error when comment info is not bytes

[narugo1992]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.89%. Comparing base (c3e2249) to head (a7a8b3e).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #103   +/-   ##
=======================================
  Coverage   98.89%   98.89%           
=======================================
  Files          99       99           
  Lines        3156     3156           
=======================================
  Hits         3121     3121           
  Misses         35       35           

Flag	Coverage Δ
unittests	98.89% <100.00%> (ø)

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