feat(exceptions): add NetworkException for connectivity failures

Signed-off-by: Vitor Mattos <vitor@php.rio>

Author: vitormattos

src/Exception/NetworkException.php

@@ -0,0 +1,23 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+declare(strict_types=1);
+
+namespace LibreCodeCoop\NfsePHP\Exception;
+
+/**
+ * Thrown when a network-level failure prevents communication with the gateway,
+ * or when the gateway returns an unparseable response.
+ */
+class NetworkException extends NfseException
+{
+    public function __construct(
+        string $message,
+        public readonly NfseErrorCode $errorCode = NfseErrorCode::NetworkFailure,
+        ?\Throwable $previous = null,
+    ) {
+        parent::__construct($message, 0, $previous);
+    }
+}