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

Job	Run time
check (1.70.0, windows-latest)	51s
check (1.70.0, ubuntu-latest)	30s
check (stable, windows-latest)	1m 34s
check (stable, ubuntu-latest)	21s
check (nightly, windows-latest)	46s
check (nightly, ubuntu-latest)	27s
	4m 29s

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