setup.cfg: Add PEP 561 py.typed marker

[cdleonard]

This is required in order to use mypy with scapy annotations in a dependent project. Otherwise you get messages like these:

error: Skipping analyzing "scapy.packet": module is installed, but missing library stubs or py.typed marker [import-untyped]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.56%. Comparing base (8461c2e) to head (991a7b8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4391      +/-   ##
==========================================
- Coverage   81.56%   81.56%   -0.01%     
==========================================
  Files         352      352              
  Lines       83897    83897              
==========================================
- Hits        68431    68429       -2     
- Misses      15466    15468       +2     

see 3 files with indirect coverage changes

[gpotter2]

Thanks for the PR !

I must say I didn't know about PEP561.... the fact that we need this is very dumb.