Setting `early_stopping_timeout` to `None` is not handled correctly

While working with FEDOT, I discovered that the `early_stopping_timeout` parameter cannot be set to `None`. Attempting to do so results in the following errors:

```
> lambda: self.generations.stagnation_time_duration >= max_stagnation_time,
'Optimisation finished: Early stopping timeout criteria was satisfied'
)
E TypeError: '>=' not supported between instances of 'float' and 'datetime.timedelta'

../../golem/core/optimisers/populational_optimizer.py:75: TypeError
```
when `timeout` parameter is set and

```
> lambda: self.generations.stagnation_time_duration >= max_stagnation_time,
'Optimisation finished: Early stopping timeout criteria was satisfied'
)
E TypeError: '>=' not supported between instances of 'float' and 'NoneType'

../../golem/core/optimisers/populational_optimizer.py:75: TypeError
```
when both `early_stopping_timeout` and `timeout` parameters are `None`

## Current Workaround:
Currently, to disable this parameter, one can use `early_stopping_timeout=np.inf` instead.

## Expected Behavior:

Setting `early_stopping_timeout=None` should:

- Be accepted as a valid parameter value
- Effectively disable the early stopping timeout functionality