test: Add cake static analyser.

[iphydf]

This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 73.07%. Comparing base (b03b571) to head (3de7954).
Report is 3 commits behind head on master.

❗ Current head 3de7954 differs from pull request most recent head a0745ab. Consider uploading reports for the commit a0745ab to get more accurate results

Files	Patch %	Lines
toxcore/group_chats.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2724      +/-   ##
==========================================
- Coverage   73.14%   73.07%   -0.08%     
==========================================
  Files         149      149              
  Lines       30516    30517       +1     
==========================================
- Hits        22320    22299      -21     
- Misses       8196     8218      +22     

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