Fix: Correct Client State Management in LaravelHttpTransport

[CodeWithKyrian]

This PR addresses a bug in LaravelHttpTransport that caused issues with tracking active clients, leading to "inactive or unknown client" errors when attempting to send messages.

Problem:

The LaravelHttpTransport previously maintained an internal, in-memory $activeClients array. In a standard Laravel request-response environment (without persistent workers like Octane), this transport instance is re-created for almost every HTTP interaction (initial SSE GET, message POSTs, SSE stream polls). This meant the in-memory $activeClients list was unreliable and often out of sync with the actual client state managed by ClientStateManager (which uses a persistent cache).

As a result, even if ClientStateManager knew a client was active (e.g., after client_connected was emitted in the SSE GET request), a subsequent sendToClientAsync call triggered by a server-side event might find the $activeClients array empty in the new transport instance handling that server-side logic, leading to failed message delivery.

Solution:

1. Removed the internal $activeClients array from LaravelHttpTransport.
2. Removed the client_connected and client_disconnected event listeners within LaravelHttpTransport that were managing this local array. Client connection and disconnection events are still emitted for the Protocol layer to handle with ClientStateManager.
3. LaravelHttpTransport::sendToClientAsync now directly queues messages via ClientStateManager without checking the local $activeClients array.
4. The existing message event listener in LaravelHttpTransport that calls clientStateManager->updateClientActivity() remains, as this is the correct way to signal activity to the persistent state manager.

Closes #13