Make functions with mutable references safe #949

Job	Run time
fmt / fmt	11s
msrv (windows-latest)	47s
cross (macos-latest, stable)	2m 46s
cross (macos-latest, nightly)	2m 54s
cross (ubuntu-latest, stable)	1m 58s
cross (ubuntu-latest, nightly)	2m 28s
msrv (ubuntu-latest)	46s
clippy / clippy	38s
windows_gnu (nightly, x86_64-pc-windows-gnu)	1m 29s
wine	1m 35s
security_audit / security_audit	11s
test (windows-latest, beta)	1m 42s
test (ubuntu-latest, nightly)	1m 2s
test (macos-latest, nightly)	1m 3s
test (macos-latest, beta)	57s
test (ubuntu-latest, stable)	51s
test (macos-latest, stable)	1m 7s
test (windows-latest, stable)	1m 35s
test (ubuntu-latest, beta)	51s
test (windows-latest, nightly)	1m 58s
	26m 49s

Provide feedback