Bump csfixer to version 3.75.0 and tweak configuration

[micheleorselli]

Apart from updating php cs fixer to the latest version a few new rules have been added:

1. use self::assert* in phpunit test
2. use array<something> in docblocks
3. add PER-CS, which is supposed to be an evolving standard to keep up with new language features

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.47%. Comparing base (58d222a) to head (4f61982).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #479      +/-   ##
============================================
+ Coverage     95.35%   95.47%   +0.11%     
  Complexity      640      640              
============================================
  Files            73       73              
  Lines          1723     1723              
============================================
+ Hits           1643     1645       +2     
+ Misses           80       78       -2     

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[AlessandroMinoccheri]

LGTM 👍