Feature/xarray to grib from temporal accumulation

[sandorkertesz]

No description provided.

[sandorkertesz]

This PR fixes the following Xarray to GRIB conversion issue.

Generate the data:

• GRIB forecast data containing step ranges converted to Xarray with time_dim_mode="valid_time"
• the Xarray is converted back to GRIB

Problems:

• the generated GRIB contains an inconsistent time section: dataData/Time + step != validityData/Time
• as a consequence, when the GRIB is converted to Xarray with time_dim_mode="valid_time" there is a crash: "ValueError: Input does not form a full hypercube. Expected number of fields based on the dimensions does not match actual number of fields"

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.74%. Comparing base (66cddef) to head (135eff3).
⚠️ Report is 135 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #735      +/-   ##
==========================================
- Coverage   90.02%   85.74%   -4.29%     
==========================================
  Files         158      172      +14     
  Lines       12086    13242    +1156     
  Branches      593      643      +50     
==========================================
+ Hits        10881    11354     +473     
- Misses       1023     1698     +675     
- Partials      182      190       +8     

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