[FIX] crm: Fix compute method on day open

Step to reproduce : Import from Excel a list of Opportunities.

The problem is that in _compute_day_open, the abs of the extraction
date_open - create_date is set as the lead's day_open.
As the date_open has no milliseconds, all those records which
create date is the same second have a date_open that is before their create_date.

Fixed it by comparing the date_create and date_open without microsecond.

Task ID 2222251

closes odoo/odoo#50431

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>