Would it be possible to support a mutationKeyHashFn option?

[lsmurray]

My keys can contain bigInt which isn't JSON serializable. I don't have direct control over the keys since I'm using connect-query-es. These keys are not compatible with the default hashKey. I can provide my own hashKey implementation using queryKeyHashFn but there is no similar option for mutation keys. If you're cool with it I'll provide a PR adding the mutationKeyHashFn following the same patterns and tests used by the queryKeyHashFn implementation.

@TkDodo tagging you since you've been quite quick responding to these previously and I'm willing to put up a PR.

[TkDodo]

sorry for the late reply; yeah I think it would be good to have that for consistency 👍