Add support for anemoi-datasets

[sandorkertesz]

This PR adds support for anemoi-datasets.

Major changes

1. New properties/methods added to Field:

• mars_grid
  for a latlon grid returns [dx,dy] otherwise metadata("gridName")
• mars_area
  returns [north, west, south, east]
• resolution

     if grid_type in ("reduced_gg", "reduced_rotated_gg"):
         return self.metadata.get("gridName")
  
     if grid_type == "regular_ll":
         x = self.metadata.get("DxInDegrees")
         y = self.metadata.get("DyInDegrees")
         assert x == y, (x, y)
         return x
  
     if grid_type == "lambert":
         x = self.metadata.get("DxInMetres")
         y = self.metadata.get("DyInMetres")
         assert x == y, (x, y)
         return str(x / 1000).replace(".", "p") + "km"

• grid_points()
  returns (lats, lons)
• grid_points_unrotated()
• rotation

     return (
            self.metadata.get("latitudeOfSouthernPoleInDegrees"),
            self.metadata.get("longitudeOfSouthernPoleInDegrees"),
            self.metadata.get("angleOfRotationInDegrees"),
        )

2. Added new FieldList type: FieldArray. Name should be reviewed since earthkit-data already has ArrayFieldList

3. Added the FieldCube and Cubelet classes. A version of it already exists in the feature/tensor branch.

4. The "valid_datetime" metadata key now returns a str instead of datetime.datetime

5. Add dependency on earthkit-geo

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.63%. Comparing base (08a404b) to head (c94f37d).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #383      +/-   ##
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- Coverage    89.75%   89.63%   -0.13%     
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  Files          119      119              
  Lines         7515     7513       -2     
  Branches       662      662              
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- Hits          6745     6734      -11     
- Misses         640      649       +9     
  Partials       130      130              

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[iainrussell]

It feels a little strange to return a str rather than a datetime here. Could the client (anemoi-datasets) not perform the conversion to string?

[sandorkertesz]

This requires further discussion.

[iainrussell]

Would be nice to have a little description of what Patch is for

[iainrussell]

It's not clear to me why we need this, it does not seem to be used in earthkit.data. Is it used directly by anemoi-datasets, and what does it address that the current FieldList does not?

[sandorkertesz]

With it you can create a fieldlist out of a set/list of fields. FieldList does not store a list of fields (it is more generic) so cannot do it.

[sandorkertesz]

It is used directly in anemoi-datasets.

[iainrussell]

Not all grids will have these metadata keys (e.g. Lambert), but I guess we'd want to fail for these ones anyway