Add IsExternalInit type, BaseCmdlet class, and SessionStatus enum

Introduce the IsExternalInit type for C# 9 records compatibility in .NET Standard 2.1. Implement BaseCmdlet class to provide common functionality for cmdlets, including methods for writing results and handling async operations. Add SessionStatus enum to represent API session states.

classlib/enum/SessionStatus.cs

@@ -0,0 +1,22 @@
+namespace PS.IPAM;
+
+/// <summary>
+/// Represents the current status of an API session.
+/// </summary>
+public enum SessionStatus
+{
+    /// <summary>
+    /// No session exists or no token is available.
+    /// </summary>
+    NoSession,
+
+    /// <summary>
+    /// The session token has expired.
+    /// </summary>
+    Expired,
+
+    /// <summary>
+    /// The session is valid and ready for use.
+    /// </summary>
+    Valid
+}