m: Fix memory issue bykeeping the slot persistent #346

Job	Run time
msrv (1.63, 1.63)	1m 21s
fmt	12s
clippy	16s
cross (ubuntu-latest)	1m 23s
cross (macos-latest)	1m 7s
security_audit	11s
windows_gnu (nightly, x86_64-pc-windows-gnu)	1m 10s
test (ubuntu-latest, nightly)	35s
test (ubuntu-latest, stable)	31s
test (windows-latest, nightly)	1m 7s
test (windows-latest, stable)	1m 28s
test (macos-latest, nightly)	48s
test (macos-latest, stable)	24s
	10m 33s

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