Add must_use function attributes #1664

Job	Run time
Test (miri)	10m 0s
Test (Ubuntu, MSRV)	3m 48s
Test (Windows, MSRV)	5m 15s
Type-check benchmarks	18s
Test (MacOS, MSRV)	5m 13s
Type checking (MSRV, no_std)	3m 50s
Test (Ubuntu, stable)	1m 2s
Type checking (MSRV, std_no_offset)	5m 27s
Test (Windows, stable)	2m 15s
Clippy	55s
Type checking (MSRV, std_with_offset)	4m 27s
Test (MacOS, stable)	1m 23s
Type checking (stable, no_std)	44s
Type checking (stable, std_no_offset)	2m 19s
Cross-build	30s
Type checking (stable, std_with_offset)	1m 21s
Documentation	14s
Formatting	14s
Coverage	57s
Publish docs	0s
	50m 12s

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