Baker: Update DAL attestable slots worker streams

What

Parent MR: !19875 (merged)

This MR wires the DAL attestable slots worker into the baker lifecycle so delegate subscriptions stay up-to-date. We still do not change the baker pipeline: the baker still builds/proposes/attests exactly as before, we only maintain background subscriptions.

Main integration points:

• Startup (for long-running baker in baking_scheduling and for client bake for command implemented in baking_lib) : register profiles + subscribe current delegates.
• Per-level: refresh subscriptions for next-level delegates.

Why

To keep the worker's cache warm and current without touching the critical path. Eventually, when we swap baker's DAL attestable slots retrieval mechanism to use the worker's one, we need the cache to be already sufficiently populated, and to avoid any network delays during the critical vote/attestation/forging path.

How

Manually testing the MR

CI green (this should be a no-op)

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