Prepare version 3.2

[dfremont]

Preparation for a 3.2.0b1 release to support VerifAI 3. This PR just bumps the version number and adds a few type annotations to fix a warning from VerifAI (which was no longer able to infer the type of Car.height because of the improved system for CARLA object dimensions).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.83%. Comparing base (8257147) to head (a10801e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #485      +/-   ##
==========================================
- Coverage   89.87%   89.83%   -0.05%     
==========================================
  Files          48       48              
  Lines       13346    13346              
==========================================
- Hits        11995    11989       -6     
- Misses       1351     1357       +6     

see 3 files with indirect coverage changes

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