[Bug]: DLIB uses a small sliding window even when the upsampling limit is set to 0

### What Operating System(s) are you seeing this problem on?

Windows

### dlib version

19.24.99

### Python version

3.9.13

### Compiler

GCC 6.3.0

### Expected Behavior

I expect when the up-sampling limit is 0 then DLIB would use a sliding window that is approximately same as the bounding boxes that I have marked. I can't see any way of setting the sliding window size manually and this seems to be a major problem.

How is this sliding window dimension automatically picked up?

### Current Behavior

The sliding window size is significantly smaller than the bounding boxes I have marked even when the up-sampling limit is set to 0. I can't set this window manually.

### Steps to Reproduce

Here is the training.xml file

```

imglab dataset
Created by imglab tool.

```

As you can see, all the bounding boxes are of the same dimension. That's why I was expecting that up-sampling is not required and DLIB will just use the sliding window dimension same as the bounding boxes.

The training code is similar to that of the example provided.

### Anything else?

_No response_