Remove instructions from base agent type, and ensure description is only required where necessary. (#154)

* Remove instructions from base agent type, and ensure description is only required where necessary.

* Fix code issue.

* Remove unused import.

* Remove typo

* Make the description parameter optional

* Also use name for handoffs if no description is provided.

dotnet/src/Microsoft.Extensions.AI.Agents.Runtime.Abstractions/ActorMetadata.cs

@@ -15,7 +15,7 @@ public readonly struct ActorMetadata : IEquatable<ActorMetadata>
     /// <param name="type">The type of the actor.</param>
     /// <param name="key">The unique key associated with the actor.</param>
     /// <param name="description">A brief description of the actor.</param>
-    public ActorMetadata(ActorType type, string key, string description)
+    public ActorMetadata(ActorType type, string key, string? description = null)
     {
         if (!ActorId.IsValidKey(key))
         {
@@ -46,7 +46,7 @@ public readonly struct ActorMetadata : IEquatable<ActorMetadata>
     /// <summary>
     /// A brief description of the actor's purpose or functionality.
     /// </summary>
-    public string Description { get; }
+    public string? Description { get; }
 
     /// <inheritdoc/>
     public override readonly bool Equals(object? obj) =>

dotnet/src/Microsoft.Extensions.AI.Agents.Runtime.Abstractions/RuntimeActor.cs

@@ -53,7 +53,7 @@ public abstract class RuntimeActor : IRuntimeActor
     protected RuntimeActor(
         ActorId id,
         IAgentRuntime runtime,
-        string description,
+        string? description = null,
         ILogger? logger = null)
     {
         this.Id = id;