Cross-check refine checks against the Gray Paper

Follow-up task from PR #859: https://github.com/FluffyLabs/typeberry/pull/859

The initial implementation of refine needs to be cross-checked against the Gray Paper specification to ensure all checks and validations are correct and complete.

Requested by: @tomusdrw
Reference: https://github.com/FluffyLabs/typeberry/pull/859#discussion_r