Shell & plugin: delegators contribution RPC

Implements the delegators_contribution RPC

Tests are in !17186

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

Summary by CodeRabbit

• New Features
  • Introduced a new RPC endpoint for retrieving detailed information on a baker’s delegation contributions for a specified cycle.
• Refactor
  • Consolidated logic for unstake requests to improve modularity and reliability.
  • Streamlined the retrieval of delegators and delegation summaries, enhancing clarity and maintainability.