implement parser for label

[cm-ayf]

#3 に含まれるstruct Phonemeの変更が必要（別PRにする？） #5

[codecov]

Codecov Report

Attention: 70 lines in your changes are missing coverage. Please review.

Comparison is base (3a168bf) 0.00% compared to head (10e15b9) 81.62%.

❗ Current head 10e15b9 differs from pull request most recent head 569156e. Consider uploading reports for the commit 569156e to get more accurate results

Files	Patch %	Lines
src/parser/mod.rs	71.89%	52 Missing ⚠️
src/serializer/mod.rs	90.81%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main       #4       +/-   ##
=========================================
+ Coverage      0   81.62%   +81.62%     
=========================================
  Files         0        2        +2     
  Lines         0      381      +381     
=========================================
+ Hits          0      311      +311     
- Misses        0       70       +70     

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