DM-38845: Fix row group computation crash if a list in a DataFrame is serialized to parquet.

[erykoff]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Patch coverage: 92.30% and no project coverage change.

Comparison is base (9b39f79) 87.76% compared to head (83e8218) 87.77%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #828   +/-   ##
=======================================
  Coverage   87.76%   87.77%           
=======================================
  Files         268      268           
  Lines       35008    35032   +24     
  Branches     7368     7375    +7     
=======================================
+ Hits        30726    30748   +22     
- Misses       3124     3125    +1     
- Partials     1158     1159    +1     

Impacted Files	Coverage Δ
python/lsst/daf/butler/formatters/parquet.py	93.67% <71.42%> (-0.38%)	⬇️
tests/test_parquet.py	99.16% <100.00%> (+0.01%)	⬆️

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[jbkalmbach]

Looks Good! Fixes issues I found in ts_wep with dataframes and specifically dataframes with empty lists (which are now included in the tests here).