Fix jlabel parser/serializer bugs

[femshima]

ref: jpreprocess/jpreprocess#219

• E5/G5の論理が逆になっていたので，直しました．
• B2,B3,C2,C3,D2,D3は1桁で出力する必要がありますので，これも直しました．

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a5ef2d6) 91.43% compared to head (c072a5d) 93.28%.

❗ Current head c072a5d differs from pull request most recent head 11b29a8. Consider uploading reports for the commit 11b29a8 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   91.43%   93.28%   +1.84%     
==========================================
  Files           8        8              
  Lines         981     1013      +32     
==========================================
+ Hits          897      945      +48     
+ Misses         84       68      -16     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.