When querying across two points in time this describes the change
between the two points: ADDED, REMOVED, or ACTIVE. If there was no
compare_duration supplied in the request the state change will be:
UNUSED
Values:
UNUSED (0):
State change is unused, this is the canonical
default for this enum.
ADDED (1):
Asset was added between the points in time.
REMOVED (2):
Asset was removed between the points in time.
ACTIVE (3):
Asset was present at both point(s) in time.
