refactor: store initial assets in class variable

[dfguerrerom]

this PR creates a new mutable class member _initial_assets: list which will be filled with a list of assets after the first instance creation of the AssetSelect. This member will be checked before running the ee.data.listassets call to earthengine, if the member has already data, the elements will use their data instead.

I also moved the decorator as I proposed in #931

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.77%. Comparing base (776f019) to head (5fcd958).
Report is 2 commits behind head on main.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #932   +/-   ##
=======================================
  Coverage   96.76%   96.77%           
=======================================
  Files          39       39           
  Lines        3960     3964    +4     
=======================================
+ Hits         3832     3836    +4     
  Misses        128      128           

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