Baker: Use monitoring RPC for forging DAL attestation

What

Parent MR: !19877 (merged)

In this MR we switch the baker to read DAL attestable slots from the attestable slots worker cache instead of calling the static DAL node RPC on the critical path. We keep may_get_dal_content wait-free, as no network I/O or subscription happens inside getters. We also keep baker’s external behaviour unchanged, this MR only changes the data source used to compute the attestation bitset.

Why

Previously the baker queried at n + lag − 2 and carried that status forward to be included at n + lag − 1 and finally baked at n + lag (where n is the published_level).

With the worker, the baker obtains attestable slots at n + lag − 1 directly from the DAL stream (i.e., one level in advance, not two). This reduces look-ahead, aligns timing with when the info is actually available, and avoids extra polling.

How

Manually testing the MR

1. CI green

2. tezt-cloud experiments - journal

3. Manual testing

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.
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