docs: update docs for NodeConfigData class

lib/src/core/utils/daemon_manager/node_config_data.dart

@@ -1,7 +1,27 @@
+/// [NodeConfigData] Documentation:
+/// `NodeConfigData` is a singleton class that stores and manages
+/// configuration data related to a Pactus blockchain node initialization .
+///
+/// ## Features:
+/// - Implements the Singleton pattern to ensure a single instance.
+/// - Provides getters and setters for essential configuration properties.
+/// - Stores working directory, restoration seed, password, and validator
+/// quantity.
+///
+/// ## Usage:
+/// ```dart
+/// final config = NodeConfigData.instance;
+/// config.workingDirectory = "/path/to/dir";
+/// print(config.workingDirectory);
+/// ```
+///
+/// ## Notes:
+/// - Default values are empty strings to prevent null issues.
 class NodeConfigData {
-  // Private constructor
+  // Private constructor to enforce the Singleton pattern
   NodeConfigData._internal();
-  // Singleton instance
+
+  /// The single instance of [NodeConfigData]
   static final NodeConfigData instance = NodeConfigData._internal();
 
   // Private variables
@@ -10,13 +30,13 @@ class NodeConfigData {
   String? _password;
   String? _validatorQty;
 
-  // Getters
+  // Getters - return empty strings if values are null
   String get workingDirectory => _workingDirectory ?? '';
   String get restorationSeed => _restorationSeed ?? '';
   String get password => _password ?? '';
   String get validatorQty => _validatorQty ?? '';
 
-  // Setters
+  // Setters - update private variables
   set workingDirectory(String value) {
     _workingDirectory = value;
   }