Update to pandas 2

[crusaderky]

Blockers:

• Pin pandas < 2 pydata/xarray#7650

The blocker can be circumvented by doubling environments in CI, one with xarray+pandas 1.5 and another with pandas 2 and no xarray.

[mrocklin]

Anything still blocking this? Are we waiting for an xarray release for example? If so, what is the timeline on that?

[crusaderky]

@mrocklin we're waiting on https://github.com/coiled/support-capital-one/issues/33

[mrocklin]

I wouldn't expect that to resolve any time in the immediate future, and I'd certainly like to move forward and see how Pandas 2 improvements impact benchmarks much sooner.

I'd recommend dropping Python 3.8 in benchmarks and moving on. I don't think that we need to resolve the question of when Dask drops support for Python 3.8 in order to evolve benchmarks forward.