Implementation of the localize_options tool.

Returns the accepted options for a formatter function with their types, allowed values, defaults, and descriptions. Backed by curated metadata files at priv/mcp/options/<module>.exs — each file evaluates to a map from {function_name, arity} to a list of option specs.

Each option spec has the shape:

%{
  name: :locale,
  type: "atom() | String.t() | Localize.LanguageTag.t()",
  allowed_values: nil,             # or a list of atoms / strings
  default: ":en",
  description: "The locale to format under."
}

When no metadata file exists for a module the tool returns the raw @spec lifted via Code.fetch_docs/1 so the caller still gets a useful answer — just with allowed_values: nil everywhere. Manually curated entries take precedence.