The previous filters didn't take timezones into account, and
returned stringified naive datetime values in local browser
time. Those would then be interpreted by the server-side as
UTC date, and depending on the current timezone offset vs UTC,
yield partially incorrect results.
By returning directly a datetime.datetime object instead of
a stringified version (see previous commit 76881fb),
we can get the expected result regarless of the timezone.
Fixes#2972Closes#6229
opw-621282
Nicolas Lempereur
81a3f56651