Add borders param to descale

[LightArrowsEXE]

Zewia linked this package in SeaDex earlier today, claiming it helps resolve issues with messy edges pretty well. It's probably a good idea to explore these claims and see whether we can incorporate them into our own descale tool if they appear beneficial.

[LightArrowsEXE]

Did a bit of testing, and the results seem pretty alright.

    descaled1 = BicubicSharp.descale(clip_y, **de_args)
    descaled2 = bdescale(clip_y, c=1, left=3, right=3, bottom=0, top=0, **de_args)

While they're not perfect, this alone seems to help a lot in suppressing ugly edge ringing. We should perform more testing, but for now I'm happy enough with these results to urge we add a similar functionality to descale.