Resolve Tests-007..012 code-review findings

Tests-007: TestServerCallContext and stream-writer/constraint helpers were
copy-pasted across five test files. Consolidated into a shared
MxGateway.Tests.TestSupport namespace; duplicates deleted.

Tests-008: renamed snake_case alarm-test methods to PascalCase
Method_Condition_Result and dropped redundant usings. Re-triaged two
inaccurate sub-claims (the "wnwrap" name and a required CompilerServices
using).

Tests-009: corrected three copy-paste-mismatched XML <summary> comments in
SessionManagerTests.

Tests-010: added the missing anonymous-localhost security negatives —
bypass disallowed, and loopback-allowed from a remote address.

Tests-011: SessionWorkerClientFactoryFakeWorkerTests discarded worker tasks.
The test class now tracks each launcher and observes its task in DisposeAsync.

Tests-012: added xunit.runner.json pinning collection parallelism and
documented the ephemeral-port convention.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/MxGateway.Tests/Gateway/Sessions/NotWiredAlarmRpcDispatcherTests.cs

@@ -1,5 +1,3 @@
-using System.Threading;
-using System.Threading.Tasks;
 using MxGateway.Contracts.Proto;
 using MxGateway.Server.Sessions;
 
@@ -15,7 +13,7 @@ namespace MxGateway.Tests.Gateway.Sessions;
 public sealed class NotWiredAlarmRpcDispatcherTests
 {
     [Fact]
-    public async Task AcknowledgeAsync_returns_ok_with_worker_pending_diagnostic()
+    public async Task AcknowledgeAsync_WhenNotWired_ReturnsOkWithWorkerPendingDiagnostic()
     {
         IAlarmRpcDispatcher dispatcher = new NotWiredAlarmRpcDispatcher();
 
@@ -33,11 +31,11 @@ public sealed class NotWiredAlarmRpcDispatcherTests
         Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
         Assert.Equal("session-1", reply.SessionId);
         Assert.Equal("corr-1", reply.CorrelationId);
-        Assert.Contains("worker", reply.DiagnosticMessage, System.StringComparison.OrdinalIgnoreCase);
+        Assert.Contains("worker", reply.DiagnosticMessage, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]
-    public async Task QueryActiveAlarmsAsync_yields_no_snapshots()
+    public async Task QueryActiveAlarmsAsync_WhenNotWired_YieldsNoSnapshots()
     {
         IAlarmRpcDispatcher dispatcher = new NotWiredAlarmRpcDispatcher();