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 :white_check_mark:

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

Additional details and impacted files

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

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