Accept string-like tags responding to to_str

additionally, disallow `Array` arguments

Author: rsamoilov

lib/rage/configuration.rb

@@ -300,8 +300,8 @@ class LogTags < LogContext
     private
 
     def validate_input!(obj)
-      if !obj.is_a?(Array) && !obj.is_a?(String) && !obj.respond_to?(:call)
-        raise ArgumentError, "custom log tags has to be an Array, String, or Proc"
+      if !obj.respond_to?(:to_str) && !obj.respond_to?(:call)
+        raise ArgumentError, "custom log tags has to be a String or a Proc"
       end
     end
   end
@@ -595,7 +595,7 @@ def __finalize
     end
 
     if @log_tags
-      Rage.__log_processor.add_custom_tags(@log_tags.objects.flatten)
+      Rage.__log_processor.add_custom_tags(@log_tags.objects)
     end
   end
 end

lib/rage/log_processor.rb

@@ -65,6 +65,8 @@ def build_custom_tags_proc
     calls = @custom_tags.map.with_index do |tag_object, i|
       if tag_object.is_a?(String)
         "@custom_tags[#{i}]"
+      elsif tag_object.respond_to?(:to_str)
+        "@custom_tags[#{i}].to_str"
       else
         "@custom_tags[#{i}].call"
       end