feat: Wire in-service RPC core for ctx.rpc.call

[doubleailes]

Summary

Builds on #155 (the async handler / RpcContext refactor) to make ctx.rpc.call(...) actually work.

• New girolle/src/rpc_core.rs — RpcCallerCore owns a per-service reply queue (rpc.listener-<service-uuid>), a publish channel, and a DashMap<correlation_id, oneshot::Sender<PayloadResult>> correlation map. new() declares the queue, starts a delegate that drains correlations into the map, and returns Arc<Self>.
• RpcCaller now holds Option<Arc<RpcCallerCore>> plus the parent delivery's FieldTable. pub async fn call(service, method, payload) -> GirolleResult<Value> is live. Per-delivery, the consumer derives a caller via with_parent_headers(inbound_headers) so nameko.call_id_stack propagates from the parent. nameko.AMQP_URI is always stamped; the stack is seeded with the service identifier when the parent had none.
• RpcService startup calls RpcCallerCore::new(&conn, conf, id) once and stores the resulting caller in SharedData.
• Adds dashmap = 6.1 and the proxy_service example forwarding proxy.hello → video.hello from inside its handler.

Known limitations (deferred)

• Pending entries with no reply leak forever; no timeout yet.
• Outbound call_id_stack is propagated as-is from the parent — Python Nameko also stamps the parent service's outbound call entry on the way out. Cosmetic; the chain is still continued correctly by the target.
• EventDispatcher still inert — that's the next PR.

Test plan

• cargo build --workspace
• cargo build --examples (incl. new proxy_service)
• cargo test --workspace --lib (14 passed)
• cargo test --workspace --doc (30 + 1 passed)
• cargo clippy --workspace --all-targets
• Smoke test: run `simple_macro` + `proxy_service` against RabbitMQ; call `proxy.hello` and confirm reply matches `video.hello`'s output.

🤖 Generated with Claude Code

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