Modernize notebook resource and extension load

[philippjfr]

Implements #8290

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.23%. Comparing base (d93db73) to head (fd62e2d).

Files with missing lines	Patch %	Lines
panel/io/resources.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8291      +/-   ##
==========================================
- Coverage   70.26%   70.23%   -0.03%     
==========================================
  Files         348      348              
  Lines       54646    54601      -45     
==========================================
- Hits        38395    38349      -46     
- Misses      16251    16252       +1     

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