feat: complete remaining jetstream parity implementation plan

tests/NATS.Server.Tests/JetStreamSnapshotRestoreApiTests.cs

@@ -0,0 +1,17 @@
+namespace NATS.Server.Tests;
+
+public class JetStreamSnapshotRestoreApiTests
+{
+    [Fact]
+    public async Task Snapshot_then_restore_reconstructs_messages()
+    {
+        await using var fx = await JetStreamApiFixture.StartWithStreamAsync("ORDERS", "orders.*");
+        _ = await fx.PublishAndGetAckAsync("orders.created", "1");
+
+        var snap = await fx.RequestLocalAsync("$JS.API.STREAM.SNAPSHOT.ORDERS", "{}");
+        snap.Snapshot.ShouldNotBeNull();
+
+        var restore = await fx.RequestLocalAsync("$JS.API.STREAM.RESTORE.ORDERS", snap.Snapshot!.Payload);
+        restore.Success.ShouldBeTrue();
+    }
+}