Tezlink/Node: Fix Tezlink backend

What

Fix tezlink backend, functions that uses the store where implemented but as the Tezlink backend was not overwrite it was never used. This MR also introduces in block_storage_sig a function to read a block hash at a certain level (with its implementation in case we use the store)

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