One compiled field spec inside a Dextrin.Schema.Compiled struct.
required comes from the ?-suffixed key convention (a field key
ending in ? is optional; no separate flag exists in .dxns itself
— reusing DXN's own identifier grammar rather than adding one);
default/description only ever come from the %field{...} escape
hatch, since optionality is already fully covered by the key suffix.
Summary
Types
@type t() :: %Dextrin.Schema.Field{ default: term() | :none, description: String.t() | nil, name: String.t(), required: boolean(), type: Dextrin.Schema.TypeExpr.t() }