Add agentic request-response example

[GautamBytes]

Description

Add a new standalone example on top of libp2p.request_response that demonstrates a simple agent workflow using two one-shot request/response exchanges:

1. capability_query
2. store_intent

The example should be Filecoin-aligned in naming and semantics, but fully local to py-libp2p. It should not call Synapse SDK, Filecoin services, or any external providers.

Motivation

The new libp2p.request_response helper currently has a generic JSON example, but there is no higher-level example showing how to build an agent-style control plane on top of it.

This example should demonstrate:

• capability discovery
• structured task submission
• validation and rejection paths
• partial-success results
• deterministic, inspectable responses over real libp2p streams

Requirements

• add an example-local protocol module for message validation and deterministic simulation
• add a runnable demo that:
  • starts a listener without -d
  • connects and sends capability_query then store_intent with -d
• use a single protocol ID with a "type" discriminator
• simulate Filecoin-aligned storage semantics:
  • size validation
  • metadata limits
  • root vs session-key style authorization
  • provider catalog with one unhealthy provider
  • complete, partial, and rejected result states
• register a console script for the example
• add docs page + examples index entry
• add focused tests for validation logic and host-to-host integration

Open questions

No response

Are you planning to do it yourself in a pull request ?

Yes