refactor: prefers using mix.exs for application env defaults

lib/tower.ex

@@ -218,8 +218,6 @@ defmodule Tower do
 
   alias Tower.Event
 
-  @default_reporters [Tower.EphemeralReporter]
-
   @doc """
   Determines if a process exit `reason` is "normal".
 
@@ -450,7 +448,7 @@ defmodule Tower do
   end
 
   defp reporters do
-    Application.get_env(:tower, :reporters, @default_reporters)
+    Application.fetch_env!(:tower, :reporters)
   end
 
   defp async(fun) do

lib/tower/logger_handler.ex

@@ -1,7 +1,6 @@
 defmodule Tower.LoggerHandler do
   @moduledoc false
 
-  @default_log_level :critical
   @handler_id Tower
   @own_logs_domain [:tower, :logger_handler]
 
@@ -101,7 +100,7 @@ defmodule Tower.LoggerHandler do
   defp log_level do
     # This config env can be to any of the 8 levels in https://www.erlang.org/doc/apps/kernel/logger#t:level/0,
     # or special values :all and :none.
-    Application.get_env(:tower, :log_level, @default_log_level)
+    Application.fetch_env!(:tower, :log_level)
   end
 
   defp safe_log(level, message) do

mix.exs

@@ -30,6 +30,10 @@ defmodule Tower.MixProject do
   def application do
     [
       extra_applications: [:logger, :inets],
+      env: [
+        reporters: [Tower.EphemeralReporter],
+        log_level: :critical
+      ],
       mod: {Tower.Application, []}
     ]
   end