allow bounds of {eq: key}

[ianmacartney]

Currently if your aggregate key is not an array, prefix doesn't work (gives an opaque type error).
Instead, allow doing eq since this is likely what you want.

And don't allow "prefix" when the key is not an array.

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npm i https://pkg.pr.new/get-convex/aggregate/@convex-dev/aggregate@159

commit: 69691cd