feat/agentic-request-response-example

[GautamBytes]

Summary

• add a new agentic request-response example that performs capability_query followed by store_intent over fresh one-shot streams
• add an example-local protocol/simulation module for Filecoin-aligned limits, provider selection, partial-success behavior, and simulated auth handling
• register the new agentic-request-response-demo console script and document it in the examples docs
• add focused tests for validation paths and host-to-host integration

Closes: #1294

Depends on: #1286
This PR is stacked on the secure request/response helper work and should be merged after #1286.

Details

• keeps the libp2p.request_response library API unchanged
• models a control-plane workflow only; it does not call Synapse, Filecoin nodes, or external providers
• includes deterministic simulated providers, piece IDs, dataset IDs, and .invalid retrieval URLs so the example is explicit about being local-only

Manual verification

• ran the listener/dialer flow locally
• confirmed status: complete with default copies
• confirmed status: partial and one unhealthy-provider failure with --copies 3

Notes

• adds the matching newsfragment for issue #1294
• this example is intentionally local-only and simulates Filecoin-style control-plane behavior without calling Synapse SDK, Filecoin services, or external providers