Simplify proj params

[tylere]

Simplifies how the desired pixel grid information is specified when opening of datasets.
Previously, crs, scale, projection and geometry were available as parameters.
With this change crs, crs_transform, and shape_2d are used to specify the grid.
See #217 for the rational for this change.

Other changes:

• Adds pixi package manager configuration files (useful for developers who use pixi)
• Limits Python to 3.12 (to avoid version conflicts among dependencies)
• Updates the README code examples

Note that this PR does not update code in the examples/ folder.

[jakenotjay]

Hi @jdbcode and @tylere do you think this will get merged anytime soon? I'm implementing a connector between XEE and icechunk that is covering a lot of ground that would be covered by the changes here. In the discussion where this was first proposed, the idea of mirroring similar parameters such as the odc geobox would be super helpful, as I'm building my models around the geobox too and I'm finding it non-trivial to perfectly align the grid that I have client side and the grid that XEE provides using the geometry parameters.

If there are final review changes required around the affine package etc. I'm happy to help on that front too.

[jdbcode]

I'm going to try to make progress on the unresolved comments over the next week and a half. I'll give an update later next week.

[jdbcode]

@tylere and @naschmitz, the outstanding comments have been addressed (see the last batch of commits). All of the unit and integration tests are passing and the readme has been updated to reflect changes (also expanded).

I'm hoping that you two can take a quick look before the end of the week and then we merge it. Since it is not merging into main, I suggest we continue any additional work that might need to be done when it is in the google:simplify_pixel_grid_params branch.

[naschmitz]

This is amazing! Thank you!

[tylere]

Thank you @jdbcode and @naschmitz !