Always reencode using our presets (even for high quality) and choose best format

[benoit74]

Fix #356

Changes

• simplify choosing best format from youtube to be sure to have a format with highest resolution possible in all cases to avoid problems while re-encoding
• always reencode (even for high quality) using our presets, to simplify things (otherwise it is too much dependent on Youtube choices in terms of resolution and codecs and bitrates, hard to follow)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 1.25%. Comparing base (b4ec53f) to head (92976e5).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/src/youtube2zim/scraper.py	0.00%	5 Missing ⚠️
scraper/src/youtube2zim/processing.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #373   +/-   ##
=====================================
  Coverage   1.25%   1.25%           
=====================================
  Files         11      11           
  Lines       1114    1114           
  Branches     163     163           
=====================================
  Hits          14      14           
  Misses      1100    1100           

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[rgaudin]

LGTM<