#2887 - Updates to Node components to use rom_config and allow for extensibility. Router and Firewall continue to have custom from_config. Some test fixes to reflect changes to functionality.

docs/source/how_to_guides/extensible_nodes.rst

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+.. only:: comment
+
+    © Crown-owned copyright 2025, Defence Science and Technology Laboratory UK
+
+.. _about:
+
+
+Extensible Nodes
+****************
+
+Node classes within PrimAITE have been updated to allow for easier generation of custom nodes within simulations.
+
+
+Changes to Node Class structure.
+================================
+
+Node classes all inherit from the base Node Class, though new classes should inherit from either HostNode or NetworkNode, subject to the intended application of the Node.
+
+The use of an `__init__` method is not necessary, as configurable variables for the class should be specified within the `config` of the class, and passed at run time via your YAML configuration using the `from_config` method.
+
+
+An example of how additional Node classes is below, taken from `router.py` withing PrimAITE.
+
+.. code-block:: Python
+
+class Router(NetworkNode, identifier="router"):
+    """ Represents a network router within the simulation, managing routing and forwarding of IP packets across network interfaces."""
+
+    SYSTEM_SOFTWARE: ClassVar[Dict] = {
+        "UserSessionManager": UserSessionManager,
+        "UserManager": UserManager,
+        "Terminal": Terminal,
+    }
+
+    network_interfaces: Dict[str, RouterInterface] = {}
+    "The Router Interfaces on the node."
+    network_interface: Dict[int, RouterInterface] = {}
+    "The Router Interfaces on the node by port id."
+
+    sys_log: SysLog
+
+    config: "Router.ConfigSchema" = Field(default_factory=lambda: Router.ConfigSchema())
+
+    class ConfigSchema(NetworkNode.ConfigSchema):
+        """Configuration Schema for Router Objects."""
+
+        num_ports: int = 5
+
+        hostname: ClassVar[str] = "Router"
+
+        ports: list = []
+
+
+
+Changes to YAML file.
+=====================
+
+Nodes defined within configuration YAML files for use with PrimAITE 3.X should still be compatible following these changes.