Schema DSL for generating Rustler structs and tagged enums.

Use this when a group of Elixir structs should be mirrored in Rust. A schema module defines nodes, fields, type aliases, and tagged enums; rust_items/1 returns Rust fragments ready for rustq.exs.

defmodule MyApp.Codegen.ContentSchema do
  use RustQ.Rustler.Schema

  schema MyApp.Content do
    node Text do
      field :text, :String
      field :size, {:option, :String}
    end

    node Paragraph do
      field :body, {:vec, Content}
    end

    tagged_enum Content do
      variants :all
    end
  end
end

Field optionality is encoded in the Rust type ({:option, :String}), keeping the schema close to the generated Rust.