WIP Ensemble and some other fixes

[joshday]

• Fixed result_files to return filename rather than s3 bucket url
• handle both "timestep" and "timestamp" fields in data.
• Minor cleanup
• A start on ensemble

[codecov-commenter]

Codecov Report

Merging #103 (993adab) into main (05063a3) will increase coverage by 0.27%.
The diff coverage is 58.57%.

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@@            Coverage Diff             @@
##             main     #103      +/-   ##
==========================================
+ Coverage   78.37%   78.64%   +0.27%     
==========================================
  Files           3        3              
  Lines         356      384      +28     
==========================================
+ Hits          279      302      +23     
- Misses         77       82       +5     

Impacted Files	Coverage Δ
src/SimulationService.jl	71.10% <57.57%> (-0.13%)	⬇️
src/operations.jl	88.48% <59.45%> (-0.33%)	⬇️

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