Encoding helpers used by generated to_map/1 functions.
to_map/1
@spec big_int(integer()) :: String.t()
@spec bytes(binary()) :: String.t()
@spec list([term()], (term() -> term())) :: [term()]
@spec map(map(), (term() -> term())) :: map()
@spec nullable(term(), (term() -> term())) :: term()
@spec optional(map(), String.t(), term(), (term() -> term())) :: map()
@spec timestamp(DateTime.t()) :: String.t()