test(galaxy): isolate process-wide telemetry tests; bounded stream-cancel wait

GalaxyTelemetryTests (ActivityListener) and GatewayGalaxyDataWriterFailClosedTests
(MeterListener, filtered only by meter and instrument name) observe every Galaxy span or
measurement in the process. They now run in a collection with parallelization disabled
(F-FU6), because a parallel driver test, or its background probe seed, polluted their counts.
The stream-cancel assertion in GalaxyDriverShutdownTests goes back to a bounded wait: the
instantaneous IsCompleted check introduced in round 1 was racy.

Refs #735

Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/ProcessWideTelemetryCollection.cs

@@ -0,0 +1,17 @@
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests;
+
+/// <summary>
+///     Classes that assert on process-wide telemetry (an <c>ActivityListener</c> on the Galaxy
+///     ActivitySource, a <c>MeterListener</c> on the Galaxy meter) run with parallelization disabled:
+///     those listeners see every Galaxy span / measurement in the process, so any parallel class that
+///     drives a traced subscriber or the data writer — including a driver's background probe seed that
+///     outlives its test — pollutes their counts (F-FU6, observed flaky in lane F fix round 2).
+/// </summary>
+[CollectionDefinition(Name, DisableParallelization = true)]
+public sealed class ProcessWideTelemetryCollection
+{
+    /// <summary>The collection name.</summary>
+    public const string Name = "Process-wide Galaxy telemetry";
+}