Typed input and output

Hi! I am trying to get rid of `JSON.parse(input)` and `JSON.dump(output)` in activities/workflows and wanted to define Input and Output classes with dry-struct to define the structure.

Then I found this line in https://github.com/coinbase/temporal-ruby/blob/master/lib/temporal/concerns/typed.rb#L22

```ruby
unless klass.is_a?(Dry::Types::Type)
```

Now I am stuck on how to make reusable structs with validation for workflow/activity params. I have three questions:

1. Does it make sense to change condition in typed.rb to allow dry structs?
2. How I can add typed output, so I don't need to serialize and deserialize outputs multiple time?
3. Any best practices to validate inputs before activating the workflow?

Any ideas how to solve this?