Refactor chainable options

[ixti]

Currently, options rely on Hashes. Although those are fine, but that blows up Chainable with custom builders for those. I propose refactor all of the options to standalone classes with help of Literal gem:

class HTTP
  class Options < Literal::Struct
    prop :proxy, _Nilable(Proxy)

    class Proxy < Literal::Data
      prop :type, _Union(:http, :socks5), :positional, default: :http

      prop :host, String
      prop :port, Integer
      prop :username, _String?
      prop :password, _String?

      prop :headers, _Nilable(Headers) do |value|
        Headers.coerce(value) unless value.nil?
      end
    end

    def with(**)
      self.class.new(**self, **)
    end
  end

  module Chainable
    def via(...)
      branch options.with(proxy: Proxy.new(...))
    end
  end
end

cc: @tarcieri

[ixti]

Actually I think atm it will only benefit for Proxy, but the same idea might be applied to features as well:

module HTTP
  class Feature < Literal::Data
    def wrap_request(request)
      request
    end

    def wrap_response(response)
      response
    end

    def on_error(_request, _error); end
  end

  module Features
    class Logging < Feature
      prop :logger, _Interface(:debug, :info), default: -> { NullLogger.new }

      class NullLogger
        def info(...); end
        def debug(...); end
      end

      # ...
    end
  end
end

[tarcieri]

It would be great to address #558 in an options refactoring

[ixti]

That's was one of the things I've been thinking as well. Will try to come up with proposal for that one first then.