Fix test isolation issue in publisher spec

Reset Connection singleton between tests to prevent mock leakage.
The Connection singleton was caching the mocked JetStream context
across test examples, causing RSpec to detect double leakage when
tests ran in certain orders.

Fixes issue where 'persists exception when publish raises error'
test would fail with 'Double was originally created in one example
but has leaked into another example' error.

Author: attaradev

spec/publisher/publisher_spec.rb

@@ -10,14 +10,16 @@
 
   before do
     JetstreamBridge.reset!
+    # Reset Connection singleton to prevent mock leakage between tests
+    JetstreamBridge::Connection.instance_variable_set(:@singleton__instance__, nil)
     # Mock Connection.connect! before configure to prevent actual connection
     allow(JetstreamBridge::Connection).to receive(:connect!).and_return(jts)
     JetstreamBridge.configure do |c|
       c.destination_app = 'dest'
       c.app_name        = 'source'
       c.env             = 'test'
     end
-    allow(jts).to receive(:publish).and_return(ack)
+    allow(jts).to receive(:publish) { ack }
   end
 
   after { JetstreamBridge.reset! }
@@ -268,7 +270,7 @@
     end
 
     it 'persists exception when publish raises error' do
-      allow(jts).to receive(:publish).and_raise(StandardError, 'NATS error')
+      allow(jts).to receive(:publish) { raise StandardError, 'NATS error' }
       expect(outbox_repo).to receive(:persist_exception).with(record, kind_of(StandardError))
 
       result = publisher.publish(resource_type: 'user', event_type: 'created', payload: payload)