Make changes to parcel manager to handle string date

The server will now send string instead of usec, so this CL parses the
date string back to a base::Time. Doing this will allow it easier for
UI to format the time object to a localized string, compared to just
storing the "yyyy-mm-dd" string.
Also, changed the parcel manager to only send get status request to
server if the parcels are not done, as there is no need to update
parcel status if it is already delivered.

Bug: 1488558
Change-Id: Id8195b442535ddc5f65edb99cea832e430c9940f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4901825
Commit-Queue: Min Qin <qinmin@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1204081}