Implement compat layer for baggage

[fractalwrench]

Goal

Works towards #276 by creating a compat module implementation for the Baggage interface.

Testing

Added unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.56%. Comparing base (a583254) to head (b1d905f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
+ Coverage   89.82%   90.56%   +0.74%     
==========================================
  Files         264      266       +2     
  Lines        3429     3308     -121     
  Branches      369      370       +1     
==========================================
- Hits         3080     2996      -84     
+ Misses        265      228      -37     
  Partials       84       84              

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