multiboot2: streamlined tag getters #1045

Job	Run time
build (msrv) / rust	23s
build (nightly) / rust	25s
build (stable) / rust	13s
build no_std (stable) [Windows] / rust	1m 18s
build no_std (stable) [w/o builder] / rust	15s
build no_std (stable) / rust	25s
style (stable) / rust	14s
build no_std (msrv) / rust	26s
style (msrv) / rust	18s
build no_std (nightly) / rust	29s
style (nightly) / rust	25s
tests with miri (nightly) / rust	1m 19s
	6m 10s

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