Enable complete Tasks extension conformance coverage (#1741)

Copilot-Session: 7c99928c-a943-49f4-9a63-8b04a0e4d18b

src/ModelContextProtocol.Extensions.Tasks/Server/McpTaskExecutionMode.cs

@@ -0,0 +1,16 @@
+namespace ModelContextProtocol.Extensions.Tasks;
+
+/// <summary>
+/// Specifies how a tool call participates in the MCP Tasks extension.
+/// </summary>
+public enum McpTaskExecutionMode
+{
+    /// <summary>The tool always executes synchronously.</summary>
+    Synchronous,
+
+    /// <summary>The tool executes as a task when the client declares the Tasks extension.</summary>
+    Optional,
+
+    /// <summary>The tool requires the client to declare the Tasks extension.</summary>
+    Required,
+}