Avoid large chunks in climate_statistics preprocessor function with period='full'

[bouweandela]

Description

Avoid very large chunks in climate_statistics preprocessor function when used with period=full.

Issue reported in ESMValGroup/ESMValTool#3244 (comment)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.44%. Comparing base (801ffba) to head (716cf76).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2404   +/-   ##
=======================================
  Coverage   94.44%   94.44%           
=======================================
  Files         246      246           
  Lines       13743    13745    +2     
=======================================
+ Hits        12979    12981    +2     
  Misses        764      764           

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[schlunma]

Thanks @bouweandela! Let's include this in v2.11.0.