We can now derive `Eq` and `PartialEq` for structs containing callbacks #411

Job	Run time
check (1.70.0, windows-latest)	35s
check (1.70.0, ubuntu-latest)	56s
check (stable, windows-latest)	1m 21s
check (stable, ubuntu-latest)	20s
check (nightly, windows-latest)	35s
check (nightly, ubuntu-latest)	22s
	4m 9s

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