feat(dict): introduce the usage property

[kanru]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 89.20000% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.13%. Comparing base (fdfb78a) to head (a110f54).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/dictionary/usage.rs	42.85%	16 Missing ⚠️
src/dictionary/loader.rs	91.93%	5 Missing ⚠️
src/zhuyin/syllable.rs	33.33%	4 Missing ⚠️
src/dictionary/layered.rs	95.34%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #801      +/-   ##
==========================================
- Coverage   92.24%   92.13%   -0.11%     
==========================================
  Files          37       38       +1     
  Lines        9267     9385     +118     
==========================================
+ Hits         8548     8647      +99     
- Misses        719      738      +19     

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