Implement GCode M66 (Immediate mode only) #746

Job	Run time
tests (ubuntu-latest, tests)	2m 44s
build (ubuntu-latest, noradio)	1m 59s
tests (macos-latest, tests)	2m 40s
build (ubuntu-latest, wifi)	2m 7s
tests (windows-latest, tests_nosan)	3m 36s
build (ubuntu-latest, bt)	2m 8s
build (macos-latest, noradio)	1m 28s
build (macos-latest, wifi)	1m 54s
build (macos-latest, bt)	1m 34s
build (windows-latest, noradio)	5m 47s
build (windows-latest, wifi)	4m 55s
build (windows-latest, bt)	5m 1s
	35m 53s

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