Difference operators in statistics action

[tweska]

Added both difference operators from: https://codes.ecmwf.int/grib/format/grib2/ctables/4/10/

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.73228% with 21 lines in your changes missing coverage. Please review.

Project coverage is 54.18%. Comparing base (199e3ea) to head (b42f8c6).

Files with missing lines	Patch %	Lines
...c/multio/action/statistics/operations/Difference.h	69.23%	8 Missing ⚠️
...o/action/statistics/operations/InverseDifference.h	69.23%	8 Missing ⚠️
src/multio/action/statistics/Operations.h	60.00%	4 Missing ⚠️
...sts/multio/action/statistics/testStatisticsUtils.h	96.96%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #60      +/-   ##
===========================================
+ Coverage    53.21%   54.18%   +0.97%     
===========================================
  Files          218      223       +5     
  Lines        14813    15062     +249     
  Branches      1222     1246      +24     
===========================================
+ Hits          7882     8162     +280     
+ Misses        6931     6900      -31     

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[MircoValentiniECMWF]

Add seed to the random vector

[MircoValentiniECMWF]

Like the default 42