make exists a type predicate

[codingedgar]

🚀 Feature request

Current Behavior

export declare const exists: <A>(predicate: Predicate<A>) => (ma: Option<A>) => boolean

Desired Behavior

export declare const exists: <A>(predicate: Predicate<A>) => (ma: Option<A>) => ma is Some<A>

Who does this impact? Who is this for?

exists does not provide enough information to typescript, which prevents narrowing when used with libraries like ts-pattern or in plain code.

Describe alternatives you've considered

I'm not sure if this is enough or if another function might be better, because if exists returns false it doesn't mean ma is not Some<A>, but if it return true, it must be, right?

Your environment

Software	Version(s)
fp-ts	2.16.2
TypeScript	5.6.0-beta