chore: Expose request-response protocol to application layer

[crStiv]

Closes #3871

This PR:

• Implements request-response protocol for network layer
• Adds new types for network requests and responses
• Exposes network functionality to application layer through RequestHandler trait
• Implements basic request types (LeafByHeight, PayloadByVidCommitment, etc.)

This PR does not:

• Implement specific request handlers for all request types (will be added based on application needs)
• Add comprehensive error handling (will be addressed in follow-up PRs)

Key places to review:

• crates/hotshot/src/networking/request_response.rs - New protocol implementation
• crates/hotshot/src/networking/mod.rs - Module exports and organization

How to test this PR:

• Currently includes only type definitions and traits
• Unit tests will be added in follow-up commits