feat(quic): replace probe UDP data plane with QUIC datagrams

backend/tests/MoShiro.TestSupport/AgentSimulator.cs

@@ -97,6 +97,7 @@ public sealed class AgentSimulator : IAsyncDisposable
             ["meta"] = new JsonObject
             {
                 ["probe_tcp_port"] = 7443,
+                ["probe_quic_ports"] = new JsonArray(7443),
                 ["probe_udp_ports"] = new JsonArray(7443),
                 ["public_host"] = publicHost,
                 ["kinds"] = new JsonArray((kinds ?? ["udp_echo", "tcp_echo", "udp_train", "connect", "hold", "tcp_bulk", "icmp_echo"]).Select(k => (JsonNode?)JsonValue.Create(k)).ToArray()),
@@ -154,7 +155,8 @@ public sealed class AgentSimulator : IAsyncDisposable
                 TlsPublicKey = Convert.ToBase64String(_tlsKey.PublicKeySpki),
                 Addresses = Addresses is null ? null : [.. Addresses],
                 ProbeTcpPort = 7443,
-                ProbeUdpPorts = [7443],
+                ProbeQuicPorts = [7443],
+                LegacyProbeUdpPorts = [7443],
                 LocalLimits = new LocalLimits { MaxTotalMbps = 200, MaxTotalPps = 20_000, MaxConcurrentTests = 1 },
             },
             MoShiroJsonContext.Default.AgentHelloMeta);