refactoring: add type hints

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[codecov]

Codecov Report

Attention: Patch coverage is 99.19679% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.97%. Comparing base (6dedfbf) to head (f93bac5).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
trafilatura/feeds.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #723      +/-   ##
==========================================
+ Coverage   98.90%   98.97%   +0.06%     
==========================================
  Files          21       21              
  Lines        3482     3501      +19     
==========================================
+ Hits         3444     3465      +21     
+ Misses         38       36       -2     

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