Add description within visualisation (#742)

This makes it easier to understand visualization.

## Before

```mermaid
        flowchart TB
  dora-microphone
  dora-vad
  dora-distil-whisper
  dora-rerun[/dora-rerun\]
subgraph ___dora___ [dora]
  subgraph ___timer_timer___ [timer]
    dora/timer/secs/2[\secs/2/]
  end
end
  dora/timer/secs/2 -- tick --> dora-microphone
  dora-microphone -- audio --> dora-vad
  dora-vad -- audio as input --> dora-distil-whisper
  dora-distil-whisper -- text as original_text --> dora-rerun
```

## After

```mermaid
        flowchart TB
  dora-microphone[**dora-microphone**<hr/>*Microphone sending samples of audio data*]
  dora-vad[**dora-vad**<hr/>*Voice Activity Detection using Sidero model filtering audio samples into audio samples including voice.*]
  dora-distil-whisper[**dora-distil-whisper**<hr/>*Whisper model able to transcribe audio.*]
  dora-rerun[/**dora-rerun**<hr/>*Real time visualisation using Rerun.*\]
subgraph ___dora___ [dora]
  subgraph ___timer_timer___ [timer]
    dora/timer/secs/2[\secs/2/]
  end
end
  dora/timer/secs/2 -- tick --> dora-microphone
  dora-microphone -- audio --> dora-vad
  dora-vad -- audio as input --> dora-distil-whisper
  dora-distil-whisper -- text as original_text --> dora-rerun
```

libraries/core/src/descriptor/visualize.rs

@@ -72,29 +72,41 @@ fn collect_dora_nodes(
 
 fn visualize_node(node: &ResolvedNode, flowchart: &mut String) {
     let node_id = &node.id;
+    let description = if let Some(desc) = &node.description {
+        format!("<hr/>*{desc}*")
+    } else {
+        "".to_string()
+    };
+
     match &node.kind {
-        CoreNodeKind::Custom(node) => visualize_custom_node(node_id, node, flowchart),
+        CoreNodeKind::Custom(node) => visualize_custom_node(node_id, description, node, flowchart),
         CoreNodeKind::Runtime(RuntimeNode { operators, .. }) => {
-            visualize_runtime_node(node_id, operators, flowchart)
+            visualize_runtime_node(node_id, description, operators, flowchart)
         }
     }
 }
 
-fn visualize_custom_node(node_id: &NodeId, node: &CustomNode, flowchart: &mut String) {
+fn visualize_custom_node(
+    node_id: &NodeId,
+    description: String,
+    node: &CustomNode,
+    flowchart: &mut String,
+) {
     if node.run_config.inputs.is_empty() {
         // source node
-        writeln!(flowchart, "  {node_id}[\\{node_id}/]").unwrap();
+        writeln!(flowchart, "  {node_id}[\\\"**{node_id}**{description}\"/]").unwrap();
     } else if node.run_config.outputs.is_empty() {
         // sink node
-        writeln!(flowchart, "  {node_id}[/{node_id}\\]").unwrap();
+        writeln!(flowchart, "  {node_id}[/\"**{node_id}**{description}\"\\]").unwrap();
     } else {
         // normal node
-        writeln!(flowchart, "  {node_id}").unwrap();
+        writeln!(flowchart, "  {node_id}[\"**{node_id}**{description}\"]").unwrap();
     }
 }
 
 fn visualize_runtime_node(
     node_id: &NodeId,
+    _description: String,
     operators: &[OperatorDefinition],
     flowchart: &mut String,
 ) {