feat: port session 10 — Server Core Runtime, Accept Loops & Listeners

Ports server/server.go lines 2577–4782 (~1,881 Go LOC), implementing ~97
features (IDs 3051–3147) across three new partial-class files.

New files:
- NatsServer.Lifecycle.cs: Shutdown, WaitForShutdown, RemoveClient,
  SendLDMToClients, LameDuckMode, LDMClientByID, rate-limit logging,
  DisconnectClientByID, SendAsyncInfoToClients
- NatsServer.Listeners.cs: AcceptLoop, GetServerListener, InProcessConn,
  AcceptConnections, GenerateInfoJson, CopyInfo, CreateClient/Ex/InProcess,
  StartMonitoring (HTTP/HTTPS), AddConnectURLs/RemoveConnectURLs,
  TlsVersion/TlsVersionFromString, GetClientConnectURLs, ResolveHostPorts,
  PortsInfo/PortFile/LogPorts, ReadyForListeners, GetRandomIP, AcceptError
- Internal/WaitGroup.cs: Go-style WaitGroup using TaskCompletionSource

Modified:
- Auth/AuthTypes.cs: Account now implements INatsAccount (stub)
- NatsServerTypes.cs: ServerInfo.ShallowClone(), removed duplicate RefCountedUrlSet
- NatsServer.cs: _info promoted to internal for test access
- Properties/AssemblyInfo.cs: InternalsVisibleTo(DynamicProxyGenAssembly2)
- ServerTests.cs: 20 new session-10 unit tests (GenerateInfoJson, TlsVersion,
  CopyInfo, GetRandomIP — Test IDs 2895, 2906)

All 565 unit tests + 1 integration test pass.

reports/current.md

@@ -1,6 +1,6 @@
 # NATS .NET Porting Status Report
 
-Generated: 2026-02-26 19:18:19 UTC
+Generated: 2026-02-26 20:08:24 UTC
 
 ## Modules (12 total)
 
@@ -13,18 +13,18 @@ Generated: 2026-02-26 19:18:19 UTC
 
 | Status | Count |
 |--------|-------|
-| complete | 744 |
+| complete | 841 |
 | n_a | 82 |
-| not_started | 2754 |
+| not_started | 2657 |
 | stub | 93 |
 
 ## Unit Tests (3257 total)
 
 | Status | Count |
 |--------|-------|
-| complete | 276 |
+| complete | 278 |
 | n_a | 181 |
-| not_started | 2576 |
+| not_started | 2574 |
 | stub | 224 |
 
 ## Library Mappings (36 total)
@@ -36,4 +36,4 @@ Generated: 2026-02-26 19:18:19 UTC
 
 ## Overall Progress
 
-**1294/6942 items complete (18.6%)**
+**1393/6942 items complete (20.1%)**