Fix MMCQ bounds

[mezz]

I found a minor bounds issue that could cause problems with classifying single-color images.

I decided to add some tests that cover this case, and clean up a little.
Java version is bumped up to Java 8.

Details

In MMCQ.vboxFromPixels, it builds the initial color-space box by scanning pixels and finding min/max quantized values for red, green, and blue. Before the fix, each channel did:

if (value < min) {
    min = value;
} else if (value > max) {
    max = value;
}

For the first pixel in a solid non-black image, value < min is true, so the else if never runs. If every pixel has the same value, max never gets updated from 0. A solid red image could end up with red bounds like rmin = 31, rmax = 0, which is an invalid/inverted box.
The fix was to make min and max independent checks in MMCQ.java, so a single pixel can establish both bounds.

Impact

• Dominant color/palette extraction could return incorrect colors for uniform red, green, blue, gray, etc.
• The bug was especially visible for one-color images because there was no later different pixel to update max.

Failing tests that are now working:

• ignoresPixelsBelowAlphaThresholdForAbgr
  • Only the opaque blue pixel survives filtering. With one surviving pixel, bmin is set but bmax stays 0, so the VBox is invalid and the average comes back [4, 4, 128] instead of blue [0, 0, 255].
• keepsPixelsAtAlphaThresholdForAbgr
  • Same issue, but for a single threshold-alpha red pixel. It returns [128, 4, 4] instead of red [255, 0, 0].
• ignoresWhitePixelsWhenRequested
  • reported first White is filtered out, leaving only the red pixel. With one remaining color sample, max bounds are not set, so it returns [128, 4, 4].
• keepsWhitePixelsWhenNotIgnored
  • reported first The first pixel is white, then red. Because min/max were mutually exclusive, parts of the bounds end up excluding the white histogram bucket, so the palette collapses to one color instead of two.

[mezz]

@SvenWoltmann sorry for the ping, this might be hidden since it's not an active project