DatetimeInterval does not support open-ended intervals

[philvarner]

STAPI allows singly open-ended intervals in query (e.g., ../2024-04-23T00:00:00Z or 2024-04-23T00:00:00Z../), but the DatetimeInterval class only validates ISO8601 datetime values. Also, the validation of the datetime values should be revisited to ensure it's tightly allowing only RFC 3339 values instead of the broader class of ISO 8601 values. There is support for this more narrow validation in pystac that can be copied.

[c-wygoda]

Isn't pystac also lenient on RFC339/ISO8601 using dateutil.parser.isoparse? https://github.com/stac-utils/pystac/blob/5b72d15f8245cdabe0126680f9dda673434bf525/pystac/utils.py#L397

[philvarner]

ah, you're right, it is lenient. That part is probably fine then.