fix(javareach): maven validation and correct manifest class name parsing

[hogo6002]

Fixes a bunch of Java readability issues:

• remove com/ from stdlib prefixes
• exit program with errors if running against a non maven JAR
• handle wrapped class names in the manifest file
• replace some non-fatel error messages with debug messages to reduce noise

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.58%. Comparing base (2310a89) to head (135f971).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1708   +/-   ##
=======================================
  Coverage   64.58%   64.58%           
=======================================
  Files         157      157           
  Lines       15839    15839           
=======================================
  Hits        10229    10229           
  Misses       4932     4932           
  Partials      678      678           

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