Fix(prop): Allow optional props for prop(key)(obj) variety

[Harris-Miller]

The way prop(key)(obj) was typed was obj extends Record<K, unknown>. From typescript's point of view, this means that the object must contain the key, but not if the key was optional. The constraint that prop(key)(obj) should have is that if the key exists on obj, optional or not. To fix, Partial<Record<K, unknown>> should be used. But that's a lot of characters, { [P in K]?: unknown } is the exact same thing with less characters, so going with that

[perrin4869]

just wondering, any reason this was not merged yet?