[V2] Protocol: mark errors prop required

[skryukov]

This PR updates the protocol to standardize error handling across protocol adapters.

I want to ensure consistent behavior for the errors property across all adapter implementations:

• Laravel adapter already returns "errors": {} prop by default
• TypeScript types in core library expect errors to be present
• However, Rails adapter, for example, now includes errors prop by default

This change should help to synchronize error handling behavior across the entire protocol.