LP#2018534: treat year as numeric when retrieving item circs by year

LP#2018534: treat year as numeric when retrieving item circs by year

The open-ils.pcrud.search.circbyyr API uses EXTRACT to extract the year
from circulation timestamps.  In recent versions of Postgres, the return
type for EXTRACT was changed from double precision to numeric (thanks to
Jason Boyer for noticing this!); for obscure reasons, this causes pcrud
to return the year as a string instead of a number.  So, let's get the
staff client to force those values to be numbers before doing math with
them.

Signed-off-by: Jeff Davis <jeff.davis@bc.libraries.coop>