Mark TaskExtensions and new helpers as [Obsolete]

Marked TaskExtensions class and all its methods as [Obsolete] with guidance to implement Mediator behaviors instead. Added new [Obsolete] extension methods for null/empty checks and chaining. Introduced an [Obsolete] Exceptions class with factory methods for common exceptions. All changes are intended for legacy or transitional use only.

EnvelopeGenerator.Application/Common/Extensions/TaskExtensions.cs

@@ -5,6 +5,7 @@ namespace EnvelopeGenerator.Application.Common.Extensions;
 /// <summary>
 /// Extension methods for tasks
 /// </summary>
+[Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
 public static class TaskExtensions
 {
     /// <summary>
@@ -17,6 +18,7 @@ public static class TaskExtensions
     /// <param name="factory">Exception provider</param>
     /// <returns>The awaited result if not <c>null</c>.</returns>
     /// <exception>Thrown if the result is <c>null</c>.</exception>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static async Task<T> ThrowIfNull<T, TException>(this Task<T?> task, Func<TException> factory) where TException : Exception
     {
         var result = await task;
@@ -33,6 +35,7 @@ public static class TaskExtensions
     /// <param name="factory">Exception provider</param>
     /// <returns>The awaited collection if it is not <c>null</c> or empty.</returns>
     /// <exception cref="NotFoundException">Thrown if the result is <c>null</c> or empty.</exception>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static async Task<IEnumerable<T>> ThrowIfEmpty<T, TException>(this Task<IEnumerable<T>> task, Func<TException> factory) where TException : Exception
     {
         var result = await task;
@@ -47,32 +50,46 @@ public static class TaskExtensions
     /// <param name="task"></param>
     /// <param name="act"></param>
     /// <returns></returns>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static async Task<I> Then<T, I>(this Task<T> task, Func<T, I> act)
     {
         var res = await task;
         return act(res);
     }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    /// <param name="task"></param>
+    /// <returns></returns>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
+    public static Task<T?> FirstOrDefaultAsync<T>(this Task<IEnumerable<T>> task) => task.Then(t => t.FirstOrDefault());
 }
 
 /// <summary>
 /// 
 /// </summary>
+[Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
 public static class Exceptions
 {
     /// <summary>
     /// 
     /// </summary>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static NotFoundException NotFound() => new();
 
     /// <summary>
     /// 
     /// </summary>
     /// <returns></returns>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static BadRequestException BadRequest() => new();
 
     /// <summary>
     /// 
     /// </summary>
     /// <returns></returns>
+    [Obsolete("Implement Mediator behaviors in the Osolete .NET project.")]
     public static ForbiddenException Forbidden() => new();
 }