fix python 2 compatible helpers for nested unicode

[ucloud-bot]

BUG FIXES:

• Fix python 2 compatible helpers for nested CJK charset

[codecov-commenter]

Codecov Report

Merging #58 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #58   +/-   ##
=======================================
  Coverage   96.89%   96.90%           
=======================================
  Files          19       19           
  Lines         612      613    +1     
=======================================
+ Hits          593      594    +1     
  Misses         19       19           

Impacted Files	Coverage Δ
ucloud/core/typesystem/encoder.py	90.47% <100.00%> (+0.47%)	⬆️

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