[collection-search] start/end_date are kept after model initialization

[vincentsarago]

from stac_fastapi.extensions.core.collection_search.request import BaseCollectionSearchPostRequest

BaseCollectionSearchPostRequest(datetime="2020-01-01T00:00:00Z/2020-01-02T00:00:00Z").end_date
>>> datetime.datetime(2020, 1, 2, 0, 0, tzinfo=datetime.timezone.utc)

BaseCollectionSearchPostRequest().end_date
>>> datetime.datetime(2020, 1, 2, 0, 0, tzinfo=datetime.timezone.utc)

stac-fastapi/stac_fastapi/extensions/stac_fastapi/extensions/core/collection_search/request.py

Lines 114 to 156 in c71a355

	@field_validator("datetime")
	@classmethod
	def validate_datetime(cls, value: str) -> str:
	"""validate datetime."""
	# Split on "/" and replace no value or ".." with None
	values = [v if v and v != ".." else None for v in value.split("/")]
	# If there are more than 2 dates, it's invalid
	if len(values) > 2:
	raise ValueError(
	"""Invalid datetime range. Too many values.
	Must match format: {begin_date}/{end_date}"""
	)
	# If there is only one date, duplicate to use for both start and end dates
	if len(values) == 1:
	values = [values[0], values[0]]
	# Cast because pylance gets confused by the type adapter and annotated type
	dates = cast(
	List[Optional[dt]],
	[
	# Use the type adapter to validate the datetime strings,
	# strict is necessary due to pydantic issues #8736 and #8762
	SearchDatetime.validate_strings(v, strict=True) if v else None
	for v in values
	],
	)
	# If there is a start and end date,
	# check that the start date is before the end date
	if dates[0] and dates[1] and dates[0] > dates[1]:
	raise ValueError(
	"Invalid datetime range. Begin date after end date. "
	"Must match format: {begin_date}/{end_date}"
	)
	# Store the parsed dates
	cls._start_date = dates[0]
	cls._end_date = dates[1]
	# Return the original string value
	return value

ref: stac-utils/stac-pydantic#172