misc improvements #1118

Job	Run time
build (msrv) / rust	16s
build (nightly) / rust	22s
build (stable) / rust	16s
style (msrv) / rust	21s
build no_std (msrv) / rust	18s
build no_std (stable) / rust	29s
build no_std (stable) [Windows] / rust	43s
style (stable) / rust	14s
build no_std (stable) [w/o builder] / rust	12s
tests with miri (nightly) / rust	2m 8s
style (nightly) / rust	21s
build no_std (nightly) / rust	24s
	6m 4s

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