feat: V2 collection tests

[jsignell]

Related Issue(s):

• Pystac v2: Get tests/v1 passing #1657

Description:

The big question that came up in this work was: do we want datetimes to be dt.datetime or iso strings? So far v2 has the DateTime protocol defined in common_metadata.py has datetimes stored as strings in extra_fields but returns them as dt.datetime when accessed as a property. This is what is used by item.properties. But SpatialExtent just uses strings

collection.extent.temporal.interval: list[list[str]] 

[gadomski]

do we want datetimes to be dt.datetime or iso strings?

My gut tells me to store and retrieve as datetimes, and only go to/from strings on (de)serialization. That implies that it's awkward to intentionally store as a string in extra_fields.

Very open to different models, though, so curious what ya'lls instincts are.

[jsignell]

I think it's actually better to include an empty list for stac_extensions. That seems like a very common pattern in stac.

[jsignell]

do we want datetimes to be dt.datetime or iso strings?

My gut tells me to store and retrieve as datetimes, and only go to/from strings on (de)serialization. That implies that it's awkward to intentionally store as a string in extra_fields.

Very open to different models, though, so curious what ya'lls instincts are.

I think your instincts are good. I updated this PR make all the regular datetime fields convert to dt.datetime on initialization and when setting. I didn't do this for collection.extent.temporal.interval yet because it looked like there was some intentional logic there. Also because of rounding you can't guarantee that roundtripping from str -> dt.datetime -> str will give exactly the same string. Probably not super important, but if we are trying to not mutate on read...

[ircwaves]

This looks good. A question and suggestion.

[jsignell]

@gadomski do you want to take a look at this one? I think it would be best to merge it before working on item_collection and catalog tests.

[gadomski]

LGTM! Sorry about the slowness on review