treewide: code improvements and other stuff #436

Job	Run time
build (nightly) / rust	21s
build no_std (stable) [Windows] / rust	1m 44s
build (msrv) / rust	2m 38s
build (stable) / rust	14s
style (stable) / rust	41s
build no_std (stable) [w/o builder] / rust	26s
build no_std (stable) / rust	30s
build no_std (nightly) / rust	35s
style (nightly) / rust	38s
build no_std (msrv) / rust	34s
style (msrv) / rust	32s
	8m 53s

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