xarray revolution

[sbenthall]

Continuing discussion from here: https://github.com/econ-ark/HARK/pull/1283#issuecomment-1595065727

Perhaps we should use xarray data types everywhere, such as:

• grids
• distributions
• solutions
• as typed inputs/outputs to equations used in model definitions

@alanlujan91 has modeled this with Labeled distributions and several of the Consumer models already.

I propose (tentatively) that we work these changes throughout the library, rather than reserving them for special 'Labeled' classes.