Improve subsampling and dataset downloads

[nikhilwoodruff]

Fixes #2322
Fixes #2321

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 75.37%. Comparing base (58241ba) to head (b484710).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
...ngine_api/jobs/calculate_economy_simulation_job.py	28.57%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2323      +/-   ##
==========================================
- Coverage   77.16%   75.37%   -1.80%     
==========================================
  Files          88       88              
  Lines        3377     3484     +107     
  Branches      366      395      +29     
==========================================
+ Hits         2606     2626      +20     
- Misses        703      788      +85     
- Partials       68       70       +2     

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[anth-volk]

Apologies for the delay in review @nikhilwoodruff. This looks good to me, but I'll let you merge (or modify) in case there's been any change in need here, given some other subsampling-related changes we've made.