[FEAT] Add Gaussian Blur to RawImage

[BritishWerewolf]

The reason for this, is for models like U2Net where the input image size is 320x320, meaning that the resulting output needs to be resized, and can have sharp edges; blurring before resizing can smooth this out.

This is the code that I used to generate the images.

const kernels = [5, 9, 17];
const sigmas = [2, 3, 5];
const chunk = 4;
for (let i = 0; i < kernels.length; i++) {
    const kernel = kernels[i];
    const sigma = sigmas[i];
    image
        .gaussianBlur(kernel, sigma, chunk)
        then(image => image.save(`blurred-(${kernel}-${sigma}).png`));
}

Sigma should roughly be a third of kernel size (from what I found researching).
Kernel must be odd, since we want an even square around the pixel.
For example, if we had a 3x3 kernel grid, then when we place this on our pixel there is an even space all around that pixel (in this case 1 pixel).

Here is a demo of what this implementation currently looks like.

Image	Kernel	Sigma	1 chunk	4 chunks	12 chunks
	N/A	N/A	N/A	N/A	N/A
	5	2	9 seconds	3 seconds	3 seconds
	9	3	31 seconds	4 seconds	5 seconds
	17	5	1 minute, 42 seconds	8 seconds	7 seconds

[BritishWerewolf]

The reason for this, is because a kernel is essentially a square that is applied to every pixel in an image.

Consider a grid of 5x5, it would look like this, with our pixel (P) in the middle.

. . . . .
. . . . .
. . P . .
. . . . .
. . . . .

Here, it is clear to see that there is an even spacing around the pixel.

Now, consider what would happen if we used an even kernel size of 4.

. . . .
. . . .
. . P .
. . . .

The pixel does not sit neatly in the middle of the kernel and this is a problem.