Chain/block directory refactorings

This MR proposes several refactoring for the chain and block RPC directories. It paves the way toward the introduction of !9490. Indeed, in this MR we must be able to instantiate those directory at to places with different configurations for:

• RPCs that requires the block_validator -- relying on the node's side
• RPCs that do not need the block_validator -- relying on the rpc_process

The naming makes the directories pretty explicit to instantiate, however, do not hesitate to propose a better naming.

Manually testing the MR

Green CI

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