Add SPI and merge zephyr_(serial|i2c) into busio #17481

Job	Run time
scheduler	2m 33s
docs	4m 13s
windows	4m 19s
windows-zephyr (windows-2025)	4m 5s
mpy-cross-mac	28s
windows-zephyr (windows-2022)	4m 6s
mpy-cross / build (static-mingw)	53s
mpy-cross / build (static-aarch64)	54s
mpy-cross / build (static)	24s
tests / run (native)	46s
tests / run (mpy)	38s
tests / run (native_mpy)	36s
mpy-cross / build (static-raspbian)	44s
tests / run (all)	1m 13s
ports	0s
	25m 52s

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