fix: free chewing objects with chewing_free

[kanru]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 52.29%. Comparing base (71e0785) to head (9682680).
Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
src/IBusChewingLookupTable.c	83.33%	1 Missing ⚠️
src/ibus-chewing-engine.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #241      +/-   ##
==========================================
- Coverage   53.14%   52.29%   -0.86%     
==========================================
  Files          17       17              
  Lines        2081     2096      +15     
==========================================
- Hits         1106     1096      -10     
- Misses        975     1000      +25     

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