Fix inconsistency with formatter_opts type

lib/logger_json.ex

@@ -204,8 +204,8 @@ defmodule LoggerJSON do
       |> Keyword.get(:metadata, [])
       |> configure_metadata()
 
-    formatter_opts = Keyword.get(config, :formatter_opts, %{})
-    formatter_state = apply(formatter, :init, [formatter_opts])
+    formatter_opts = Keyword.get(config, :formatter_opts, [])
+    formatter_state = formatter.init(formatter_opts)
 
     %{
       state

lib/logger_json/formatter.ex

@@ -11,7 +11,7 @@ defmodule LoggerJSON.Formatter do
 
   Returned list will be used as formatter_state in `format_event/6`.
   """
-  @callback init(Keyword.t()) :: Keyword.t()
+  @callback init(Keyword.t()) :: term()
 
   @doc """
   Format event callback.

lib/logger_json/formatters/datadog_logger.ex

@@ -32,8 +32,9 @@ defmodule LoggerJSON.Formatters.DatadogLogger do
   @processed_metadata_keys ~w[pid file line function module application span_id trace_id otel_span_id otel_trace_id]a
 
   @impl true
-  def init(formatter_opts \\ %{}) do
-    opts = Map.merge(@default_opts, formatter_opts)
+  def init(formatter_opts) do
+    # Notice: we also accept formatter_opts for DataDog logger as a map for backwards compatibility
+    opts = Map.merge(@default_opts, Map.new(formatter_opts))
 
     unless is_binary(opts.hostname) or opts.hostname in [:system, :unset] do
       raise ArgumentError,

mix.exs

@@ -2,7 +2,7 @@ defmodule LoggerJSON.Mixfile do
   use Mix.Project
 
   @source_url "https://github.com/Nebo15/logger_json"
-  @version "5.1.1"
+  @version "5.1.2"
 
   def project do
     [