Etherlink/Kernel: also reject blueprints from the past in the DAL case

Context

In !15636 (merged), a check has been added for sequencer blueprints at parsing time; if their level is prior to the current block head then they are considered invalid. Unfortunately, this new check was only applied in the case where the blueprint was sent through the inbox. For blueprints sent through the DAL, another parsing function was used and not touched by !15636 (merged).

Depends on !15926 (merged).

What, why, and how

This MR adds the new check in the DAL case and factorizes the checks between the two parsing functions to avoid a similar divergence to be reintroduced in the future.

Manually testing the MR

$ cargo test dal::tests::test_parse_slot_with_blueprints_from_the_past

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR