Since [1], the test that ensures live chat threads are sorted according to their last interrest date is broken. Indeed, the sort was moved from `im_livechat` to `website_livechat`. This is incorrect. Also, most of the compare functions used to sort by datetime were incorrect: those datetimes can be undefined in which case the result of the compare function would be `NaN`. This PR moves back the sort function in the correct module and introduce a standard way to compare by datetime which handles undefined datetimes correctly. [1]: https://github.com/odoo/odoo/pull/143382 fixes runbot-47784 closes odoo/odoo#146805 Related: odoo/enterprise#53065 Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>