Revert "Breaking change to remove RRID from CORES packages (#740)"

[czarte]

This reverts commit a151e96.

---

Note

Reintroduces return-route IDs into routes/CORES and plumbs them through Neighborhood and ProxyServer, updates message schemas (hostname optional, sequence/reception fields), DNS/impersonation handling, and tests.

• Routing/Core:
  • Add return-route ID (RRID) to Route (encrypted hop) with Route::id(); change Route::round_trip(...) to accept RRID.
  • ExpectedServices::RoundTrip now carries RRID; Neighborhood generates/increments RRIDs (zero-hop too) and composes responses with RRID.
  • RouteQueryMessage now uses hostname_opt; Host moved to proxy_server/protocol_pack.
• ProxyServer:
  • New AddReturnRouteMessage; store RRID→return-route metadata in TtlHashMap; attach on requests; on responses/DNS failures, extract RRID from route and use stored metadata to report services and errors.
  • ClientRequestPayload_0v1.target_hostname is Option<String>; factories default ports; server impersonators accept optional hostname.
• Dispatcher/Streams:
  • Rename fields: reception_port_opt→reception_port, sequence_number_opt→sequence_number; propagate across TransmitDataMsg, InboundClientData, readers/pools.
• Misc:
  • Simplify TtlHashMap; remove packet "describe" helpers; extensive test updates and API adjustments throughout.

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