include microseconds when decoding datetime objects

[geospatial-jeff]

Thanks for reviewing and merging!

Good point on the serialization discrepancy. The major meaningful difference to me is that the sub-second portion of the datetime is discarded during serialization. But this probably doesn't matter most of the time.

Could be fixed by changing

https://github.com/stac-utils/stac-pydantic/blob/master/stac_pydantic/shared.py#L18

to include the %f (microsecond) part.

DATETIME_RFC339 = "%Y-%m-%dT%H:%M:%S.%fZ"

Originally posted by @colecloudtostreet in #75 (comment)

[philvarner]

Also, the constant for this should be DATETIME_RFC3339 not DATETIME_RFC339 (there are 3 3s, not 2).

[philvarner]

Another major meaningful difference is that this regex is used in the Search object, so datetimes with fractional seconds in them throw an error when used by pystac-client in a query.

[vincentsarago]

should be fixed now 🙏