Add axes and get_axis_dim to BaseGrid and other cleanup

[VeckoTheGecko]

Changes:

• Added axes and get_axis_dim() to the BaseGrid class with corresponding implementations in the UxGrid and XGrid classes. Also moved ravel/unravel logic to the BaseGrid class (fixes Adding axes and get_axis_dim to BaseGrid #2056)
• Removed lon, lat, depth from the Field class
  • These attributes didn't really make sense in the unstructured context (especially now we've settled on a different API), and also weren't used in the codebase. It makes more sense for these to live on the grids anyway where needed.
• Add uxarray to pyproject.toml dependencies (25c589b)
• Other cleanup (see commit messages)

Open questions:

• @fluidnumerics-joe, the implementation of Field.depth differed from UxGrid.depth - with the former using a helper function get_vertical_location_from_dims. Is this function still needed, or can we remove it?

• Chose the correct base branch (main for v3 changes, v4-dev for v4 changes)

• Fixes Adding axes and get_axis_dim to BaseGrid #2056

• Added tests

• Added documentation

[VeckoTheGecko]

Suggested change

	Return the dimensionality (number of cells/edges) along a specific axis.
	Return the dimensionality (number of cells/faces) along a specific axis.

I think that this should be cells/faces and not 'edges'. This is what we ravel against - so edges don't really apply (since particles can't occupy that)

[fluidnumerics-joe]

@fluidnumerics-joe, the implementation of Field.depth differed from UxGrid.depth - with the former using a helper function get_vertical_location_from_dims. Is this function still needed, or can we remove it?

We can remove the helper function now that we have the understanding in UxGrid that the vertical position is explicitly relative to the vertical layers.

[erikvansebille]

Looks good; one question below