refactor(log): make BaseHandler abstract

[timreichen]

Ref: #5702
Changes
This PR makes the BaseHandler and log() method abstract.
It removes the obsolete override for log() in FileHandler and ConsoleHandler.

[codecov]

Codecov Report

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

Project coverage is 96.29%. Comparing base (d6fde64) to head (f8b1750).
Report is 27 commits behind head on main.

Files	Patch %	Lines
log/console_handler.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5737   +/-   ##
=======================================
  Coverage   96.28%   96.29%           
=======================================
  Files         474      474           
  Lines       38387    38386    -1     
  Branches     5578     5578           
=======================================
  Hits        36962    36962           
+ Misses       1383     1382    -1     
  Partials       42       42           

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[kt3k]

LGTM