fix: isolate DlqDatabase:DataDirectory per Simulator test factory instance

SimulatorWebApplicationFactory already isolated NamespaceRepository:
DataDirectory with a per-instance GUID temp dir, but never applied the
same override to DlqDatabase:DataDirectory. Every factory instance
therefore shared one on-disk SQLite file. When xUnit ran test classes
in parallel, concurrent instances raced on ApplySchemaUpgradesAsync's
check-then-act column guard, and the second ALTER TABLE ADD COLUMN
collided with "duplicate column name: CloudProvider" —
SimulatedAzureMessagesTests.PeekMessages_AzureOrdersQueue_ReturnsActiveMessages
and
SimulatedAwsMessagesTests.PeekMessages_AwsCheckoutQueue_ReturnsActiveMessages.

Reusing the same per-instance _testDataDir for DlqDatabase:DataDirectory
gives each factory its own SQLite file, making the race structurally
impossible rather than merely less likely. Verified: both previously
failing tests pass in isolation, and the full suite (1524 unit + 73
integration) passes twice back-to-back under real parallel execution.

Author: debdevops

services/api/tests/ServiceHub.IntegrationTests/Infrastructure/SimulatorWebApplicationFactory.cs

@@ -31,6 +31,7 @@ protected override void ConfigureWebHost(IWebHostBuilder builder)
                 ["Security:Authentication:Enabled"] = "false",
                 ["Cors:AllowedOrigins:0"] = "*",
                 ["NamespaceRepository:DataDirectory"] = _testDataDir,
+                ["DlqDatabase:DataDirectory"] = _testDataDir,
                 ["RateLimit:MaxRequests"] = "9999",
             });
         });