Fix failures handling

[benoit74]

Rationale

Fix #93
Fix #94
Fix #89

Changes

• raise an Exception which clearly indicates which node failed to be processed
• do not remove the future from the list of all futures (we need them for stats + display exceptions)
• add more details about the number of failures among done tasks
• log all exceptions which occurred in all tasks so that it is possible to debug all of them at once
• upgrade to zimscraperlib 3.3.1 for Many errors Cannot set the number of threads, already set #89

[codecov]

Codecov Report

Attention: Patch coverage is 23.52941% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 29.94%. Comparing base (a5b0165) to head (18c7034).

Files	Patch %	Lines
src/kolibri2zim/scraper.py	23.52%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
+ Coverage   29.69%   29.94%   +0.25%     
==========================================
  Files           6        6              
  Lines         751      758       +7     
  Branches      130      131       +1     
==========================================
+ Hits          223      227       +4     
- Misses        522      525       +3     
  Partials        6        6              

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[rgaudin]

LGTM ; please change the var name before merging