BuildFactory

[Savva-Shuliatev]

Add BuildFactory to assemble steps with a build closure (no custom Factory type required)

Summary
This PR introduces BuildFactory, a lightweight Factory implementation that lets you provide a factory via a build closure directly in StepAssembler. This removes the need to create a separate Factory type when you only need to construct a UIViewController from its Context if needed.

Motivation
Reduce boilerplate: no need to define a dedicated Factory type for simple constructors.
Improve readability: the creation logic lives next to the step configuration.
Stay fully type-safe: generics keep ViewController and Context strongly typed.

What’s included

• BuildFactory<viewcontroller, context> that conforms to Factory.
• A shorthand static constructor BuildFactory.build(...) for concise usage in StepAssembler chains.
• A StepAssemblerWithFinder extension to accept BuildFactory via .factory(.build { ... }).

Usage example
Below is a minimal example that builds ProductViewController with a String context and assembles a step using .factory(.build { ... }):

class ProductViewController: UIViewController {

    let context: String

    init(context: String) {
        self.context = context
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

@MainActor
var productScreen: DestinationStep<ProductViewController, String> {
    StepAssembler<ProductViewController, String>()
        .finder(.classFinder)
        .factory(.build { ProductViewController(context: $0) })
        .using(.replaceRoot)
        .from(.root)
        .assemble()
}