Restored spy equals/hashcode fix

[cdalexndr]

Fixes #2331

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[TimvdLippe]

We can't revert this patch, as it will break caching of classes. I thought we added a regression test for that, but I would have to double check.

In any case, we will have to fix this in a different way, although unfortunately it is unclear what that entails.

[cdalexndr]

We can't revert this patch, as it will break caching of classes

Can you provide more details about this issue?

The cache key was fixed by 4f81d4f and this revert includes that fix.

[TimvdLippe]

#2400 was reverted per #2400 (comment) in #2402 The fix was not working as intended and broke the class cache.