test(audience-sdk): extend TestFixtures with Steam / Passport / generic user ID fixtures

ImmutableAudienceTests had four inline ID fixtures around the
identity / alias write tests:

- "76561198012345": real-shape Steam community 64-bit ID, used as
  the Identify input AND as the queue-content assertion subject
- "user1": minimal generic userId for the discarded-identify test
- "steam123": generic Steam ID for the alias-write test, used as
  both Alias input and queue-content assertion subject
- "user_456": generic Passport ID for the alias-write test

Adds SteamId64, GenericUserSingleId, SteamId, PassportId to
TestFixtures and migrates the six call sites. The SteamId64 / SteamId
input-assertion pairs were the worst offenders since a typo on one
side would silently pass on the other.

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/Tests/Runtime/ImmutableAudienceTests.cs

@@ -620,22 +620,22 @@ public void Identify_FullConsent_WritesIdentifyEvent()
         {
             ImmutableAudience.Init(MakeConfig(ConsentLevel.Full));
 
-            ImmutableAudience.Identify("76561198012345", IdentityType.Steam);
+            ImmutableAudience.Identify(TestFixtures.SteamId64, IdentityType.Steam);
             ImmutableAudience.Shutdown();
 
             var queueDir = AudiencePaths.QueueDir(_testDir);
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
             Assert.IsTrue(contents.Any(c =>
-                c.Contains($"\"{MessageTypes.Identify}\"") && c.Contains("\"76561198012345\"")));
+                c.Contains($"\"{MessageTypes.Identify}\"") && c.Contains($"\"{TestFixtures.SteamId64}\"")));
         }
 
         [Test]
         public void Identify_AnonymousConsent_IsIgnored()
         {
             ImmutableAudience.Init(MakeConfig(ConsentLevel.Anonymous));
 
-            ImmutableAudience.Identify("user1", IdentityType.Steam);
+            ImmutableAudience.Identify(TestFixtures.GenericUserSingleId, IdentityType.Steam);
             ImmutableAudience.Shutdown();
 
             var queueDir = AudiencePaths.QueueDir(_testDir);
@@ -650,14 +650,14 @@ public void Alias_FullConsent_WritesAliasEvent()
         {
             ImmutableAudience.Init(MakeConfig(ConsentLevel.Full));
 
-            ImmutableAudience.Alias("steam123", IdentityType.Steam, "user_456", IdentityType.Passport);
+            ImmutableAudience.Alias(TestFixtures.SteamId, IdentityType.Steam, TestFixtures.PassportId, IdentityType.Passport);
             ImmutableAudience.Shutdown();
 
             var queueDir = AudiencePaths.QueueDir(_testDir);
             var contents = Directory.GetFiles(queueDir, AudiencePaths.QueueGlob)
                 .Select(File.ReadAllText).ToList();
             Assert.IsTrue(contents.Any(c =>
-                c.Contains($"\"{MessageTypes.Alias}\"") && c.Contains("\"steam123\"")));
+                c.Contains($"\"{MessageTypes.Alias}\"") && c.Contains($"\"{TestFixtures.SteamId}\"")));
         }
 
         // -----------------------------------------------------------------

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

@@ -92,5 +92,15 @@ internal static class TestFixtures
         internal const string GenericAliasFromId = "fromId";
         internal const string GenericAliasToId = "toId";
         internal const string GenericAliasFromShort = "from";
+
+        // Real-shape 64-bit Steam community ID. Asserts the input is carried through faithfully.
+        internal const string SteamId64 = "76561198012345";
+
+        // Generic Steam / Passport ID fixtures used by alias and consent tests.
+        internal const string SteamId = "steam123";
+        internal const string PassportId = "user_456";
+
+        // Generic single-user fixture for tests that just need any userId.
+        internal const string GenericUserSingleId = "user1";
     }
 }