Dotstar updates are slow

[rhooper]

The dotstar library could benefit from a CircuitPython helper to offload computationally expensive setitem work to.
See adafruit/circuitpython#884

[rhooper]

I have done some experimental work on this for Neopixels, see adafruit/circuitpython#884 and adafruit/Adafruit_CircuitPython_NeoPixel#27

[kattni]

@tannewt This needs to be updated to work with pixelbuf as well. There is some work here: https://github.com/rhooper/Adafruit_CircuitPython_DotStar/blob/pixelbuf/adafruit_dotstar.py

[tannewt]

@dunkmann00 want to take a stab at it?

[dunkmann00]

Sure! I don't have any dotstars to test it though. But I think it should be straight forward enough, especially since there is already some work done on it.

[tannewt]

@dunkmann00 That'd be awesome. We can find someone with DotStars to verify the code. Thanks!

[kattni]

We did it!