DM-46563: Use masked record arrays in arrow to numpy conversion

[timj]

This is #1086 with the right branch name.

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes
• (if changing dimensions.yaml) make a copy of dimensions.yaml in configs/old_dimensions

[erykoff]

Looks good with test, but a question about the typing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.69%. Comparing base (ca923c0) to head (9ea85bc).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1087   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files         360      360           
  Lines       47094    47110   +16     
  Branches     9693     9696    +3     
=======================================
+ Hits        42240    42256   +16     
  Misses       3480     3480           
  Partials     1374     1374           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.