Cleanup JNI log handler

[gavv]

Changes:

• switch from std::mutex to pthead_mutex (for Port JNI bindings from C++ to C #55)
• simplify and cleanup code

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@e9c796d). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #82   +/-   ##
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  Coverage        ?   69.84%           
  Complexity      ?       74           
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  Files           ?       23           
  Lines           ?      378           
  Branches        ?        2           
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  Hits            ?      264           
  Misses          ?      108           
  Partials        ?        6           

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