test(audience-sdk): route queue assertions through SDK constants

ImmutableAudienceTests was using inline strings to assert against captured log lines and queue file
contents:

- Has.Some.Contains("Dropping") for the dropped-event marker that Track / Identify / Alias warns
  share
- "\"purchase\"", "\"identify\"", "\"alias\"" for queue-file content checks (the wire-format
  envelope's "type" / "eventName" fields)

Adds AudienceLogs.DroppingMarker = "Dropping" so the marker has a single source of truth and the
test references it directly.

Migrates queue-file content checks to interpolate against the SDK's existing EventNames.Purchase,
MessageTypes.Identify, and MessageTypes.Alias constants so a backend rename to those wire strings
would touch one place rather than scatter across the test.

Per the user's "everything random goes in a constant" stance.

Follow-up to SDK-272 (centralisation of duplicated literals).

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/Utility/Log.cs

@@ -85,6 +85,10 @@ internal static string ConsentSyncThrew(Exception ex) =>
 
     internal static class AudienceLogs
     {
+        // Marker shared by Track / Identify / Alias dropped-event log messages.
+        internal const string DroppingMarker = "Dropping";
+
+
         // ---- Init / config validation ----
 
         internal const string InitCalledTwice =

src/Packages/Audience/Tests/Runtime/ImmutableAudienceTests.cs

@@ -323,15 +323,15 @@ public void Track_IEventMissingRequiredField_DropsWithWarn()
                 // Assert the stable parts (event-type name and trailing "Dropping")
                 // so the test survives any change to the exception type or message.
                 Assert.That(lines, Has.Some.Contains(nameof(Purchase)));
-                Assert.That(lines, Has.Some.Contains("Dropping"));
+                Assert.That(lines, Has.Some.Contains(AudienceLogs.DroppingMarker));
             }
             finally { Log.Writer = null; }
 
             ImmutableAudience.Shutdown();
             var queueDir = AudiencePaths.QueueDir(_testDir);
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
-            Assert.IsFalse(contents.Any(c => c.Contains("\"purchase\"")),
+            Assert.IsFalse(contents.Any(c => c.Contains($"\"{EventNames.Purchase}\"")),
                 "purchase event with missing required Value must be dropped, not enqueued");
         }
 
@@ -608,7 +608,7 @@ public void Track_TypedPurchase_WritesCorrectEventName()
             var queueDir = AudiencePaths.QueueDir(_testDir);
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
-            Assert.IsTrue(contents.Any(c => c.Contains("\"purchase\"")));
+            Assert.IsTrue(contents.Any(c => c.Contains($"\"{EventNames.Purchase}\"")));
         }
 
         // -----------------------------------------------------------------
@@ -627,7 +627,7 @@ public void Identify_FullConsent_WritesIdentifyEvent()
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
             Assert.IsTrue(contents.Any(c =>
-                c.Contains("\"identify\"") && c.Contains("\"76561198012345\"")));
+                c.Contains($"\"{MessageTypes.Identify}\"") && c.Contains("\"76561198012345\"")));
         }
 
         [Test]
@@ -641,7 +641,7 @@ public void Identify_AnonymousConsent_IsIgnored()
             var queueDir = AudiencePaths.QueueDir(_testDir);
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
-            Assert.IsFalse(contents.Any(c => c.Contains("\"identify\"")),
+            Assert.IsFalse(contents.Any(c => c.Contains($"\"{MessageTypes.Identify}\"")),
                 "identify should be discarded at Anonymous consent");
         }
 
@@ -657,7 +657,7 @@ public void Alias_FullConsent_WritesAliasEvent()
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
             Assert.IsTrue(contents.Any(c =>
-                c.Contains("\"alias\"") && c.Contains("\"steam123\"")));
+                c.Contains($"\"{MessageTypes.Alias}\"") && c.Contains("\"steam123\"")));
         }
 
         // -----------------------------------------------------------------