Refactor MemoryCacheExtensions and clean up HistoryController

- Introduced a static readonly field `BaseId` in `MemoryCacheExtensions.cs`.
- Refactored `GetEnumAsDictionary<TEnum>` to use expression-bodied syntax and LINQ for improved readability and efficiency.
- Removed the import statement for `Microsoft.IdentityModel.Tokens` in `HistoryController.cs`, indicating a potential shift in authentication/authorization handling.

EnvelopeGenerator.Extensions/MemoryCacheExtensions.cs

@@ -1,20 +1,16 @@
 using Microsoft.Extensions.Caching.Memory;
-using System;
 
 namespace EnvelopeGenerator.Extensions;
 
 public static class MemoryCacheExtensions
 {
+    private static readonly Guid BaseId = Guid.NewGuid();
+
     public static IDictionary<string, int> GetEnumAsDictionary<TEnum>(this IMemoryCache memoryCache)
         where TEnum : Enum
-    {
-        var dict = new Dictionary<string, int>();
-
-        foreach (TEnum role in Enum.GetValues(typeof(TEnum)))
-        {
-            dict[role.ToString()] = Convert.ToInt32(role);
-        }
-
-        return dict;
-    }
+        => memoryCache.GetOrCreate(BaseId + typeof(TEnum).FullName, _ =>
+               Enum.GetValues(typeof(TEnum))
+                   .Cast<TEnum>()
+                   .ToDictionary(e => e.ToString(), e => Convert.ToInt32(e)))
+           ?? throw new InvalidOperationException($"Failed to cache or retrieve enum dictionary for type '{typeof(TEnum).FullName}'.");
 }

EnvelopeGenerator.GeneratorAPI/Controllers/HistoryController.cs

@@ -5,7 +5,6 @@ using EnvelopeGenerator.Extensions;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Caching.Memory;
-using Microsoft.IdentityModel.Tokens;
 using static EnvelopeGenerator.Common.Constants;