Load data only once for ESMPy regridders

[bouweandela]

Description

Realize the data only once for the ESMPy regridders.

Closes ESMValGroup/ESMValTool#3590

Test recipe:

documentation:
  description: Example recipe that shows slow regridding.
  title: Example recipe that shows slow regridding.
  authors:
    - andela_bouwe
  maintainer:
    - andela_bouwe
  references:
    - acknow_project
  projects:
    - esmval

preprocessors:
  time_ocean_zonal_mean:
    custom_order: true
    climate_statistics:
      operator: mean
      period: full
    extract_levels:
      levels: [ 0,  10, 20, 50, 100, 200, 300, 500, 750, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 3750, 4000, 4250, 4500, 4750, 5000, 5250, 5500, 5750]
      scheme: linear_extrapolate
      coordinate: depth
    regrid:
      target_grid: 1x1
      scheme: nearest
    zonal_statistics:
      operator: mean

datasets:
  - dataset: CanESM5-1
    exp: piControl
    ensemble: r1i1p2f1
    grid: gn
    institute: CCCma

diagnostics:
  diagnostic1:
    variables:
      thetao:
        mip: Omon
        project: CMIP6
        timerange: 6191/6220
        preprocessor: time_ocean_zonal_mean
    scripts: null

With these changes, the recipe takes less than a minute to run on my laptop. I did not wait for the process to complete (killed it after about 10 minutes), but reportedly it takes about an hour without these changes.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.51%. Comparing base (a51da92) to head (f15cba0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2418   +/-   ##
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  Coverage   94.51%   94.51%           
=======================================
  Files         246      246           
  Lines       14020    14023    +3     
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+ Hits        13251    13254    +3     
  Misses        769      769           

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[schlunma]

Thanks Bouwe, looks great!

Would it maybe make sense to include that into v2.11.0? This sounds like a serious performance issue.

[bouweandela]

@chrisbillowsMO @ehogan Would it be possible to include this in the upcoming v2.11 release?

[valeriupredoi]

and a very good spotting, cheers @bouweandela and @schlunma