invert_colors fails for some image formats

[zzril]

Describe the bug

The invert_colors method for images internally uses ImageOps.invert(...):
src/safeds/data/image/containers/_image.py:

    def invert_colors(self) -> Image:
        """
        Return the image with inverted colors.


        Returns
        -------
        result : Image
            The image with inverted colors.
        """
        image_copy = copy.deepcopy(self)
        image_copy._image = ImageOps.invert(image_copy._image)
        return image_copy

This ImageOps.invert(...) method can fail with an obscure OSError for certain, non-RGB image formats.
For example, it fails for this image that is currently used in the image documentation.

To Reproduce

Checkout the 373-tutorial-for-image-processing branch, first commit (a3c1b1d) and run the 10th cell. (Or run everything, either in the notebook or by serving the documentation with poetry run mkdocs serve).

Expected behavior

If possible, the invert_colors method should never fail.

Stackoverflow has some tips on how to achieve that with ImageOps and non-RGB formats.

For cases where it is not possible to find a workaround, the internal error from ImageOps should be catched and a more user-friendly error should be thrown.

[zzril]

This issue currently has a draft PR (#422) linked, but no assignee. This is intentional.
The PR was created because the commit that fixes the error mentioned in this issue was needed elsewhere already.

Feel free to take over the PR and finish it.

[zzril]

The bug has been fixed in #419. Images are now converted to RGB format before inverting them.

This might mean that inverting an image twice loses some quality compared to the original image. But we do not seem to test for this, and it's in general a pretty common thing for image operations (example: resize to a smaller size, then back to original).

After having a closer look into the documentation, I also don't see any internal exceptions that could be raised when calling the PIL's convert method, so there's nothing more to do here.