wip: add steep and RBS

Steepfile

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+target :lib do
+  signature 'sig'
+
+  check 'lib'
+  ignore 'lib/dyndnsd/updater/zone_transfer_server.rb'
+
+  library 'date'
+  library 'forwardable'
+end