WIP: esp: add offset in packet protocol

This uses the reserved byte in the protocol to implement an offset. The first LED data in the packet will be drawn starting at the pixel with given offset. The rest of the pixels will stay the same. Surplus data at the end is ignored.

Untested on real hardware. Some calculations and operations were tested on the online micropython environment, to comply with the quirks of micropython. The size of the micropython.native code should not exceed its limits.