feat: support allocating public IPv6 addresses from a provider (#2162)

* feat: support allocating public IPv6 addresses from a provider

Add a provider/leaser architecture for public IPv6 address allocation
between nodes in the same network:

- A node with `--ipv6-public-addr-provider` advertises a delegable
  public IPv6 prefix (auto-detected from kernel routes or manually
  configured via `--ipv6-public-addr-prefix`).
- Other nodes with `--ipv6-public-addr-auto` request a /128 lease from
  the selected provider via a new RPC service (PublicIpv6AddrRpc).
- Leases have a 30s TTL, renewed every 10s by the client routine.
- The provider allocates addresses deterministically from its prefix
  using instance-UUID-based hashing to prefer stable assignments.
- Routes to peer leases are installed on the TUN device, and each
  client's own /128 is assigned as its IPv6 address.

Also includes netlink IPv6 route table inspection, integration tests,
and event-driven route/address reconciliation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

easytier/src/rpc_service/peer_manage.rs

@@ -3,7 +3,10 @@ use std::sync::Arc;
 use crate::{
     instance_manager::NetworkInstanceManager,
     proto::{
-        api::instance::{self, ListPeerRequest, ListPeerResponse, PeerManageRpc},
+        api::instance::{
+            self, ListPeerRequest, ListPeerResponse, ListPublicIpv6InfoRequest,
+            ListPublicIpv6InfoResponse, PeerManageRpc,
+        },
         rpc_types::controller::BaseController,
     },
 };
@@ -34,6 +37,17 @@ impl PeerManageRpc for PeerManageRpcService {
             .await
     }
 
+    async fn list_public_ipv6_info(
+        &self,
+        ctrl: Self::Controller,
+        req: ListPublicIpv6InfoRequest,
+    ) -> crate::proto::rpc_types::error::Result<ListPublicIpv6InfoResponse> {
+        super::get_instance_service(&self.instance_manager, &req.instance)?
+            .get_peer_manage_service()
+            .list_public_ipv6_info(ctrl, req)
+            .await
+    }
+
     async fn list_route(
         &self,
         ctrl: Self::Controller,