Max 339 LED chain on Pi5

I think there is an SPI buffer issue occuring on the Pi5.

I ran the code from here: https://docs.circuitpython.org/projects/neopixel_spi/en/latest/examples.html

The lit LED stops after 339 LEDs.

Increasing the SPI buffer size from default 4096 to 32768 does not help: https://stackoverflow.com/questions/16427996/increase-spi-buffer-size-in-raspbian

Start by reproducing the linked NeoPixel SPI example on a Pi 5 with a chain near 339 LEDs, then compare the behavior with the reported SPI buffer settings and the references in the issue. Done means identifying the cause of the cutoff and documenting or implementing a verified resolution for longer LED chains.

Written by the indexing model from the issue text.