feat(server): Rework transport architecture and add StreamableHttpTransport (#49)

* feat(server): Rework transport architecture and add StreamableHttpTransport

- `Server::connect()` no longer contains a processing loop.
- `TransportInterface` is updated with `setMessageHandler()` and `listen()`.
- `StdioTransport` is updated to implement the new interface.
- A new, minimal `StreamableHttpTransport` is added for stateless HTTP.

* refactor(server): use  event-driven message handling

* feat(server): Introduce a formal session management system

* fix: ensure session elements are preserved when building server (regression from #46)

* refactor: consolidate HTTP example to use shared dependencies

* feat(server): Enhance message handling with session support

- Updated `TransportInterface` to use `onMessage` for handling incoming messages with session IDs.
- Refactored `Server`, `Handler`, and transport classes to accommodate session management using `Uuid`.
- Introduced methods for creating sessions with auto-generated and specific UUIDs in `SessionFactory` and `SessionFactoryInterface`.

* feat(server): Integrate session management in message handling

- Added session support to the `Server` and `Handler` classes, allowing for session data to be managed during message processing.
- Updated `TransportInterface` to include session context in the `send` method.
- Refactored various request handlers to utilize session information, ensuring proper session handling for incoming requests.
- Introduced a file-based session store for persistent session data management

* feat: Update session builder method to use set* instead of with*

* feat: Fix test compatibility with new session management architecture

* chore: apply code style fixes

* fix: remove deprecated SSE transport and resolve PHPStan issues

examples/05-stdio-env-variables/server.php

@@ -49,11 +49,16 @@ use Mcp\Server\Transport\StdioTransport;
 
 logger()->info('Starting MCP Stdio Environment Variable Example Server...');
 
-Server::make()
+$server = Server::make()
     ->setServerInfo('Env Var Server', '1.0.0')
     ->setLogger(logger())
     ->setDiscovery(__DIR__, ['.'])
-    ->build()
-    ->connect(new StdioTransport(logger: logger()));
+    ->build();
+
+$transport = new StdioTransport(logger: logger());
+
+$server->connect($transport);
+
+$transport->listen();
 
 logger()->info('Server listener stopped gracefully.');