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

Job	Run time
check (1.60.0, windows-latest)	1m 59s
check (1.60.0, ubuntu-latest)	2m 16s
check (stable, windows-latest)	1m 1s
check (stable, ubuntu-latest)	9s
check (nightly, windows-latest)	29s
check (nightly, ubuntu-latest)	17s
	6m 11s

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