feat: add networking module with TCP Socket/Server and example applications

Implement a full-featured `net` module supporting TCP `Socket` and `Server` classes via libuv, including example applications (chat server, echo server, HTTP client/server, file explorer, system dashboard) and benchmark scripts (fibonacci, n-body). Add GEMINI.md project documentation and Stderr class to io module.

example/chat_server.wren

@@ -0,0 +1,57 @@
+// retoor <retoor@molodetz.nl>
+import "net" for Server, Socket
+import "scheduler" for Scheduler
+
+class ChatServer {
+  construct new(port) {
+    _port = port
+    _clients = []
+    _server = Server.bind("0.0.0.0", port)
+    System.print("Chat Server listening on port %(_port)")
+  }
+
+  run() {
+    while (true) {
+      var socket = _server.accept()
+      handleNewClient(socket)
+    }
+  }
+
+  handleNewClient(socket) {
+    _clients.add(socket)
+    var id = _clients.count
+    System.print("Client %(id) connected. Total: %(_clients.count)")
+
+    Fiber.new {
+      broadcast("Client %(id) joined the chat!\n", socket)
+      
+      while (true) {
+        var message = socket.read()
+        if (message == null || message == "") break
+        
+        System.print("Client %(id): %(message.trim())")
+        broadcast("Client %(id): %(message)", socket)
+      }
+
+      System.print("Client %(id) disconnected.")
+      _clients.remove(socket)
+      socket.close()
+      broadcast("Client %(id) left the chat.\n", null)
+    }.call()
+  }
+
+  broadcast(message, sender) {
+    for (client in _clients) {
+      if (client != sender) {
+        // We use a separate fiber for each write to prevent one slow 
+        // client from blocking the broadcast to others
+        Fiber.new {
+          client.write(message)
+        }.call()
+      }
+    }
+  }
+}
+
+var server = ChatServer.new(7070)
+server.run()