auction: use TriggerData for validation and simplify its api

[erwanor]

While reviewing #4254, @hdevalence noticed that the TriggerData should encapsulate the validation boundary that it implicitly relies on. That way it can be reused in the action handlers and we will be able to simplify its API and internal impl.

Thanks a lot for the review, I think this is mergeable but I agree with your comments about TriggerData. I think we want:

1. Make TriggerData inner field private
2. Enforce parameter validation via a constructor
3. Use that constructor in the action handlers
4. Drop checked operation (since we operate behind a validation boundary)

Originally posted by @erwanor in #4254 (comment)