Close cbor serde timers to accurately measure middleware timing (#578)

Author: Madrigal

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/protocol/DeserializeResponseMiddleware.java

@@ -78,6 +78,8 @@ defer endTimer()
 
                 $deserialize:W
 
+                endTimer()
+                span.End()
                 return out, metadata, nil
                 """,
                 MapUtils.of(

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/protocol/SerializeRequestMiddleware.java

@@ -82,6 +82,9 @@ defer endTimer()
 
                 $serialize:W
 
+                endTimer()
+                span.End()
+
                 return next.HandleSerialize(ctx, in)
                 """,
                 MapUtils.of(