Sky brightness inaccurate due to units error

This is for current version PyPI 0.0.2.3, on macOS Sonoma 14.5. The sky brightness input to deeplenstronomy is shown in the examples (https://deepskies.github.io/deeplenstronomy/Notebooks/ConfigFiles.html) to be:

`sky_brightness: measured light contamination from the atmosphere in magnitude per square arcsecond`

followed by,

```
SURVEY:
PARAMETERS:
BANDS: g,r,i,z,Y
seeing: 0.9
magnitude_zero_point: 30.0
sky_brightness: 23.5
num_exposures: 10

```

This indicates an input in magnitude/sq. arcsec. I believe the `sky_brightness` value is not manipulated and directly passed into `lenstronomy.Util.data_util.bkg_noise()` which takes input in counts/s/sq. arcsec, rather than magnitude/sq. arcsec. See function signature below (https://lenstronomy.readthedocs.io/en/latest/_modules/lenstronomy/Util/data_util.html):

```
def bkg_noise(
readout_noise, exposure_time, sky_brightness, pixel_scale, num_exposures=1
):
"""Computes the expected Gaussian background noise of a pixel in units of
counts/second.

:param readout_noise: noise added per readout
:param exposure_time: exposure time per exposure (in seconds)
:param sky_brightness: counts per second per unit arcseconds square
:param pixel_scale: size of pixel in units arcseonds
:param num_exposures: number of exposures (with same exposure time) to be co-added
:return: estimated Gaussian noise sqrt(variance)
"""
exposure_time_tot = num_exposures * exposure_time
readout_noise_tot = num_exposures * readout_noise**2 # square of readout noise
sky_per_pixel = sky_brightness * pixel_scale**2
sky_brightness_tot = exposure_time_tot * sky_per_pixel
sigma_bkg = np.sqrt(readout_noise_tot + sky_brightness_tot) / exposure_time_tot
return sigma_bkg
```

To test, I attach 3 images with only changing sky brightness in the .yaml file, and show that the sky brightness input is certainly acting like a counts/s input rather than a mag/sq. arcsec input.


Testing for a visible change in generated images with changing sky brightness required a `sky_brightness: 10_000` or so before it could be seen, indicating inputs should be in flux. Entering a value of 0. or 1. sky brightness should produce a very bright image for magnitude/sq. arcsec but instead produces an image with no sky noise. Similarly, entering a negative value for the sky_brightness causes nan images, which should not occur for magnitude based inputs.

I also attach .yaml files which can be used to reproduce the same (uploaded as .txt at the end). The only difference in these files is the sky_brightness parameter.

Lastly, the default survey distributions provided in distributions.py (https://github.com/deepskies/deeplenstronomy/blob/9672080cd1a5792887341f4fb13c3b0bcf913600/deeplenstronomy/distributions.py) are also in mag/sq. arcsec. This means that any use of the default survey distributions such as des_sky_brightness causes() a too-low sky brightness input to replicate the survey.

Happy to provide more information or receive corrections if I have misunderstood this.

[sky10000.txt](https://github.com/user-attachments/files/15891240/sky10000.txt)
[sky100.txt](https://github.com/user-attachments/files/15891241/sky100.txt)
[sky1.txt](https://github.com/user-attachments/files/15891242/sky1.txt)