Kernel/SDK: Mock: enforce a DAL slot to be revealable after attestation lag

What

The mock runtime keeps track of a current level, this MR simply uses it to ensure that revealing DAL slot before the attestation lag returns empty pages. Based on !14986 (merged)

Why

This will help testing Etherlink with DAL slots.

How

Manually testing the MR

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