Support for non-nanosecond datetime

[kafitzgerald]

In short, the broader ecosystem is working to support non-nanosecond datetime objects (see: pydata/xarray#7493) in Pandas 2+ and Xarray's release last month. This topic was brought to my attention by the recent upstream dev issues w/ Xarray (#681).

As I was digging through our climatology code today, I noticed we have some things hard coded that will break (in some cases) with these ecosystem changes.

We'll likely want to pin some dependencies and/or make changes and add tests to support this.

Related:

• Helpful Xarray docs on time coding
• Xarray docs on non-standard calendars and dates outside the precision range

[kafitzgerald]

It looks like we already have versions of these packages with support for non-nanosecond datetimes installing in our test environments. Our tests aren't failing, but I suspect that's because we're not testing for this.

_infer_calendar_name and the test suite are probably where changes are needed.

Also worth noting that there's some overlap here with #508.