fix(audience): lock context.libraryVersion to the SDK version

context.libraryVersion is the analytics identity of the tracking
library itself, used to segment telemetry by SDK version. It was
developer-overridable via AudienceConfig.PackageVersion, letting
arbitrary values pollute that signal. The override was also unused
internally.

Source libraryVersion from Constants.LibraryVersion at the Track /
Identify / Alias call sites and remove the public PackageVersion
property. Drift from package.json stays guarded by
ConstantsTests.LibraryVersion_MatchesPackageJson.

Breaking: removes public AudienceConfig.PackageVersion.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: nattb8

src/Packages/Audience/Runtime/AudienceConfig.cs

@@ -116,11 +116,6 @@ public class AudienceConfig
         /// </summary>
         public string? PersistentDataPath { get; set; }
 
-        /// <summary>
-        /// Library version sent on every message.
-        /// </summary>
-        public string PackageVersion { get; set; } = Constants.LibraryVersion;
-
         /// <summary>
         /// Maximum time <see cref="ImmutableAudience.Shutdown"/> waits for
         /// the final flush, in milliseconds.

src/Packages/Audience/Runtime/ImmutableAudience.cs

@@ -330,7 +330,7 @@ public static void Track(IEvent evt)
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, state.Level);
             // ToProperties returns a fresh dict per call, so no snapshot needed.
             var userId = state.Level == ConsentLevel.Full ? state.UserId : null;
-            var msg = MessageBuilder.Track(eventName, anonymousId, userId, config.PackageVersion, properties, config.TestMode);
+            var msg = MessageBuilder.Track(eventName, anonymousId, userId, Constants.LibraryVersion, properties, config.TestMode);
             EnqueueTrack(msg);
         }
 
@@ -356,7 +356,7 @@ public static void Track(string eventName, Dictionary<string, object>? propertie
 
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, state.Level);
             var userId = state.Level == ConsentLevel.Full ? state.UserId : null;
-            var msg = MessageBuilder.Track(eventName, anonymousId, userId, config.PackageVersion,
+            var msg = MessageBuilder.Track(eventName, anonymousId, userId, Constants.LibraryVersion,
                 SnapshotCallerDict(properties), config.TestMode);
             EnqueueTrack(msg);
         }
@@ -403,7 +403,7 @@ public static void Identify(string userId, IdentityType identityType, Dictionary
 
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, level);
             var msg = MessageBuilder.Identify(anonymousId, userId, identityType.ToLowercaseString(),
-                config.PackageVersion, SnapshotCallerDict(traits), config.TestMode);
+                Constants.LibraryVersion, SnapshotCallerDict(traits), config.TestMode);
             EnqueueIdentity(msg);
         }
 
@@ -434,7 +434,7 @@ public static void Alias(string fromId, IdentityType fromType, string toId, Iden
             if (config == null) return;
 
             var msg = MessageBuilder.Alias(fromId, fromType.ToLowercaseString(), toId, toType.ToLowercaseString(),
-                config.PackageVersion, config.TestMode);
+                Constants.LibraryVersion, config.TestMode);
             EnqueueIdentity(msg);
         }