feat(dict): implement CDB based user dictionary

[kanru]

In preparation to replace hash.txt and hash.dat when sqlite is not needed.

[codecov]

Codecov Report

Attention: 166 lines in your changes are missing coverage. Please review.

Comparison is base (bb05466) 79.94% compared to head (e522392) 79.83%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/dictionary/cdb.rs	58.27%	63 Missing ⚠️
src/dictionary/trie.rs	17.77%	37 Missing ⚠️
src/dictionary/kv.rs	87.55%	27 Missing ⚠️
src/dictionary/mod.rs	16.66%	25 Missing ⚠️
src/editor/estimate.rs	61.53%	5 Missing ⚠️
src/zhuyin/syllable.rs	75.00%	3 Missing ⚠️
src/conversion/mod.rs	88.23%	2 Missing ⚠️
src/dictionary/layered.rs	95.74%	2 Missing ⚠️
src/dictionary/sqlite.rs	96.66%	1 Missing ⚠️
src/editor/selection/symbol.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
- Coverage   79.94%   79.83%   -0.11%     
==========================================
  Files          55       59       +4     
  Lines       10535    11398     +863     
==========================================
+ Hits         8422     9100     +678     
- Misses       2113     2298     +185     

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