Update src/Observability/Runtime/Tracing/Contracts/SpanDetails.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: nikhilNava

src/Observability/Runtime/Tracing/Contracts/SpanDetails.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT License.
 
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 
 namespace Microsoft.Agents.A365.Observability.Runtime.Tracing.Contracts