Metadata length validation: count graphemes

[benoit74]

Fix #158
Fix #177

Changes

• Use regex module to count graphemes, it looks like the most stable and maintained package for our need
• Add utility function grapheme_count so that it can be easily reused + fixed in the future if needed
• Fix tests to exhibit the problem of graphemes vs codepoints
• Fixed type hints for images function calling PIL/pillow, which has updated its type hints in 10.4.0 and is now raising a pyright issue

[benoit74]

Edit: also had to add commit using Jeena instance just like in #175 to let the CI pass

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7ab3fcd) to head (a2c1892).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #176   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           32        32           
  Lines         1448      1452    +4     
  Branches       251       251           
=========================================
+ Hits          1448      1452    +4     

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[rgaudin]

Thank you ; please check suggestion/comment

[benoit74]

Requested changes applied, beware I did a fixup! commit which will need to be squashed before merging.