refactor: remove default value from Encoders.lookup encoding argument

Let's add it to `Encoders.new` for backward compatibility.

Author: santiagorodriguez96

lib/webauthn/encoder.rb

@@ -9,8 +9,8 @@ class Encoder
 
     def_delegators :@encoder_klass, :encode, :decode
 
-    def initialize(*args)
-      @encoder_klass = Encoders.lookup(*args)
+    def initialize(encoding = Encoders::STANDARD_ENCODING)
+      @encoder_klass = Encoders.lookup(encoding)
     end
   end
 end

lib/webauthn/encoders.rb

@@ -2,15 +2,15 @@
 
 module WebAuthn
   def self.standard_encoder
-    @standard_encoder ||= Encoders.lookup
+    @standard_encoder ||= Encoders.lookup(Encoders::STANDARD_ENCODING)
   end
 
   module Encoders
     # https://www.w3.org/TR/webauthn-2/#base64url-encoding
     STANDARD_ENCODING = :base64url
 
     class << self
-      def lookup(encoding = STANDARD_ENCODING)
+      def lookup(encoding)
         case encoding
         when :base64
           Base64Encoder