Use tap to modify new mock

Without this, mocked structs were not getting their stubs applied.
An unintended side-effect is the tap shows up in recorded calls.
This seems to be harmless, but might need to be revisited.

src/spectator/dsl/mocks.cr

@@ -294,14 +294,12 @@ module Spectator::DSL
  found_tuple = found_tuples.last %}
 
       {% if found_tuple %}
-        begin
-          %mock = {{found_tuple[2].id}}.new
+        {{found_tuple[2].id}}.new.tap do |%mock|
           {% for key, value in value_methods %}
             %stub{key} = ::Spectator::ValueStub.new({{key.id.symbolize}}, {{value}})
             %mock._spectator_define_stub(%stub{key})
           {% end %}
           ::Spectator::Harness.current?.try(&.cleanup { %mock._spectator_reset })
-          %mock
         end
       {% else %}
         {% raise "Type `#{type.id}` must be previously mocked before attempting to instantiate." %}