fix: resolve 19 JetStream test failures across 5 root causes

- HandleList: populate StreamNames/ConsumerNames alongside info lists
- ValidateConfigUpdate: allow clearing mirror/sources, accept even replicas
- ToWireFormat: add AccountInfo branch for $JS.API.INFO responses
- UpdateStream fixture: preserve existing retention policy on update
- Integration test: fix assertion to match valid account info response

tests/NATS.Server.JetStream.Tests/JetStreamApiProtocolIntegrationTests.cs

@@ -12,7 +12,7 @@ public class JetStreamApiProtocolIntegrationTests
         await using var server = await ServerFixture.StartJetStreamEnabledAsync();
         var response = await server.RequestAsync("$JS.API.INFO", "{}", timeoutMs: 1000);
 
-        response.ShouldContain("\"error\"");
+        response.ShouldContain("\"streams\"");
     }
 }