Prepare for 3.1.0 release

[lola831]

Description

Bumps the Scenic version to 3.1.0 and adds a What's New entry for this release.

Issue Link

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)

Additional Notes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.92%. Comparing base (c880a55) to head (7d8f815).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
- Coverage   89.95%   89.92%   -0.03%     
==========================================
  Files          54       54              
  Lines       13578    13578              
==========================================
- Hits        12214    12210       -4     
- Misses       1364     1368       +4     

Files with missing lines	Coverage Δ
src/scenic/core/object_types.py	93.16% <ø> (ø)

... and 4 files with indirect coverage changes

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[dfremont]

Looks good except for some nitpicks -- thanks for putting this together, Lola!

[lola831]

@dfremont I’ve pushed an update addressing all of your review comments. Thanks!

[dfremont]

Looks good, thanks Lola!