feat(p7-09): JetStream unit tests — versioning (12), dirstore (12), batching/errors deferred (66)

Port session P7-09: add tests from jetstream_versioning_test.go (T:1791–1808),
dirstore_test.go (T:285–296), jetstream_batching_test.go (T:716–744),
jetstream_errors_test.go (T:1381–1384), and accounts_test.go (T:80–110).

- JetStreamVersioningTests: 12 active unit tests + 6 deferred (server-required)
- DirectoryStoreTests: 12 filesystem tests using fake JWTs (no NKeys dependency)
- JetStreamBatchingTests: 29 deferred stubs (all require running JetStream cluster)
- JetStreamErrorsTests: 4 deferred stubs (NewJS* factories not yet ported)
- accounts_test.go T:80–110: 31 deferred (all use RunServerWithConfig)

Fix DirJwtStore.cs expiration bugs:
  - Use DateTimeOffset.UtcNow.UtcTicks (not Unix-relative ticks) for expiry comparison
  - Replace in-place JwtItem mutation with new-object replacement so DrainStale
    can detect stale heap entries via ReferenceEquals check

Add JetStreamVersioning.cs methods: SetStaticStreamMetadata,
SetDynamicStreamMetadata, CopyStreamMetadata, SetStaticConsumerMetadata,
SetDynamicConsumerMetadata, SetDynamicConsumerInfoMetadata, CopyConsumerMetadata.

Tests: 725 pass, 53 skipped/deferred, 0 failures.
DB: +24 complete, +66 deferred.

dotnet/src/ZB.MOM.NatsNet.Server/Accounts/DirJwtStore.cs

@@ -624,7 +624,7 @@ public sealed class DirJwtStore : IDisposable
     /// Deletes the JWT for <paramref name="publicKey"/> according to <see cref="_deleteType"/>.
     /// Mirrors Go <c>DirJWTStore.delete</c>.
     /// </summary>
-    private void Delete(string publicKey)
+    public void Delete(string publicKey)
     {
         if (_readonly)
         {
@@ -795,7 +795,7 @@ public sealed class DirJwtStore : IDisposable
             // Background timer — mirrors Go goroutine + time.Ticker.
             var timer = new Timer(_ =>
             {
-                var now = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() * TimeSpan.TicksPerMillisecond;
+                var now = DateTimeOffset.UtcNow.UtcTicks;
 
                 while (true)
                 {
@@ -1104,14 +1104,13 @@ internal sealed class ExpirationTracker
             // Remove old hash contribution from rolling XOR.
             XorAssign(_hash, existing.Hash);
 
-            // Update in-place.
-            existing.Expiration = exp;
-            existing.Hash = hash;
-
-            // Re-enqueue with updated priority (PriorityQueue does not support update;
-            // use a version counter approach — mark old entry stale, enqueue fresh).
-            existing.Version++;
-            _heap.Enqueue(existing, exp);
+            // Create a new JwtItem so the old heap entry becomes a stale orphan.
+            // DrainStale uses ReferenceEquals(current, top) to detect orphans:
+            // the old heap entry points to the old JwtItem object which is no longer
+            // in _idx, so it will be drained on the next PeekExpired call.
+            var updated = new JwtItem(publicKey, exp, hash);
+            _idx[publicKey] = updated;
+            _heap.Enqueue(updated, exp);
         }
         else
         {
@@ -1141,9 +1140,11 @@ internal sealed class ExpirationTracker
                 ? long.MaxValue
                 : (DateTimeOffset.UtcNow + Ttl).UtcTicks;
 
-            item.Expiration = newExp;
-            item.Version++;
-            _heap.Enqueue(item, newExp);
+            // Replace with a new JwtItem so the old heap entry becomes a stale orphan
+            // (DrainStale detects staleness via ReferenceEquals).
+            var updated = new JwtItem(publicKey, newExp, item.Hash);
+            _idx[publicKey] = updated;
+            _heap.Enqueue(updated, newExp);
         }
 
         if (EvictOnLimit)