Prevent uploading low precision timestamp when high precision one exists

[Vesihiisi]

Our upload framework will upload a date with the value YYYY even if the item already has a more precise value, like YYYY-MM-DD.

Technically this is correct behavior because a claim can have multiple values. Normally, multiple values are not uploaded if they are identified as duplicates, however in this case it is not applicable because obviously those are two different values.

Thus we need an extra check specifically for datetime values to detect whether the new value is a less precise version of the old value, in which case it should be treated as a duplicate and not uploaded.

Note that if the two values are actually different, like 1988-02-02 and 1989, they should not be treated as duplicates, as they are not different versions of the same datetime.

This is very relevant to the authority upload, as Libris contains mostly only years of authors' birth/death dates.

Task: https://phabricator.wikimedia.org/T202400