Add SPI and merge zephyr_(serial|i2c) into busio #17482

Job	Run time
scheduler	1m 1s
mpy-cross-mac	30s
windows	9m 4s
docs	55m 2s
windows-zephyr (windows-2022)	8m 57s
windows-zephyr (windows-2025)	9m 14s
tests / run (all)	1m 7s
tests / run (native)	50s
mpy-cross / build (static-mingw)	59s
tests / run (mpy)	43s
tests / run (native_mpy)	41s
mpy-cross / build (static)	18s
mpy-cross / build (static-raspbian)	49s
mpy-cross / build (static-aarch64)	42s
ports	0s
	1h 29m 57s

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