Improve types to avoid the runtime error in onetime.callCount()

[fregante]

I think onetime can return TFunction & {__onetime: true} or a Function that extends both the argument and a private OneTimedFunction type.

[sindresorhus]

Yeah, we should make it stricter.

Maybe something like:

<FunctionType extends Function>(
	fn: FunctionType,
	options?: oneTime.Options
): FunctionType & {__isOnetime: true};