Reorganize chainable timeout

Move option transformation into then block since we want to extent it.

lib/http/chainable.rb

@@ -92,18 +92,22 @@ def build_request(*args)
     #   @param [Numeric] global_timeout
     def timeout(options)
       klass, options = case options
-                       when Numeric then [HTTP::Timeout::Global, {:global => options}]
-                       when Hash    then [HTTP::Timeout::PerOperation, options.dup]
-                       when :null   then [HTTP::Timeout::Null, {}]
-                       else raise ArgumentError, "Use `.timeout(global_timeout_in_seconds)` or `.timeout(connect: x, write: y, read: z)`."
+                       when Numeric then [HTTP::Timeout::Global, {global_timeout: options}]
+                       when Hash
+                          options = options.dup
+                          %i[read write connect].each do |k|
+                            next unless options.key? k
 
-                       end
+                            options["#{k}_timeout".to_sym] = options.delete k
+                          end
 
-      %i[global read write connect].each do |k|
-        next unless options.key? k
+                          [HTTP::Timeout::PerOperation, options.dup]
+                       when :null   then [HTTP::Timeout::Null, {}]
+                       else raise ArgumentError, "Use `.timeout(:null)`, " \
+                                                 "`.timeout(global_timeout_in_seconds)` or " \
+                                                 "`.timeout(connect: x, write: y, read: z)`."
+                       end
 
-        options["#{k}_timeout".to_sym] = options.delete k
-      end
 
       branch default_options.merge(
         :timeout_class   => klass,