[Feat Request]: Coordinator instance based atom state management

[ra1028]

Checklist

• Reviewed the README and documentation.
• Checked existing issues & PRs to ensure not duplicated.

Description

Support managing a class instance with Coordinator like UIViewRepresentable instead of context.addTermination and context.keepUntilTermination.

Example Use Case

struct ExampleManagerAtom: ValueAtom, Hashable {
    final class Coordinator: ExampleDelegate {
        func delegateMethod() { ... }
    }

    func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    func value(context: Context) -> ExampleManager {
        let manager = ExampleManager()
        manager.delegate = context.coordinator
        return manager
    }
}

Alternative Solution

N/A

Proposed Solution

• Add an associated type Coordinator which is Void by default.
• Add makeCoordinator() -> Coordinator method which is empty by default.
• Maintain coordinator instance in core system and terminate it when the atom state is invalidated.

Motivation & Context

No response