Custom signals support

[MarceloPrado]

After reading the Custom Type docs, I tried creating a custom date signal. I'm not sure the right way of injecting custom assert functions. For example, the number operator adds its own set of functions. I would like to do the same for my types.

For example:

const dateSignal = signal.type<Date>(z.date().parse)

I'm trying to understand how to enhance its types to support operations besides the basic ones:

Given dates are a non-trivial type, it would be awesome if I could add operations like isSameDay, isAfter, isBefore, etc.