[FIX] calendar: recurring events have wrong end date

Steps to reproduce:
- Install Online Appointments
- Go to Calendar > Online Appointments > create a new one
- Add an available employee like "Mitchell Admin"
- Make a slot for each week day at 8:00
- Go to the Calendar of the employee and create a recurrent meeting from 6:00 to 12:00 which repeats everyday for 10 days
- Go to the Online Appointments you created then click the button "Go to Website"

Bug:
You can still make an appointment when the employee is busy.

Explanation:
Recurring events had their stop date always set to one hour after their start date. So, appointments could still be made two hours after the start date.

As seen here: https://github.com/odoo/odoo/blob/ee76b25b003f96073f78420960e216acf14bf821/addons/calendar/models/calendar.py#L47
`with_date` is passed to `timedelta()`. And passing `hours=True` works as if `True` was `1`.

```python
>>> from datetime import timedelta
>>> timedelta(hours=True)
datetime.timedelta(seconds=3600)
```

This fix reproduces the behavior before this commit introduced the bug: https://github.com/odoo/odoo/commit/9920f20e4c7753bc17bea71dea3a90f7de687196
That is, if no duration is given or duration is `0`, one hour is used instead.

This bug probably occured because of the naming of the definition: https://github.com/odoo/odoo/blob/ee76b25b003f96073f78420960e216acf14bf821/addons/calendar/models/calendar.py#L33


In fact, `with_date` can be interpreted as being boolean, and the `False` default isn't helping against that. A possibly better alternative to this could be:

```python
def calendar_id2real_id(calendar_id=None, duration=None):
```

opw:2334449

closes odoo/odoo#61823

Signed-off-by: backspac <backspac@users.noreply.github.com>