add error recovery to s3 attachment uploader

Author: realark

braintrust-sdk/src/main/java/dev/braintrust/trace/AttachmentProcessor.java

@@ -140,7 +140,7 @@ private static Pattern buildHeuristic() {
     String processAndUpload(String json) {
         if ((!config.autoConvertAIAttachments())
                 || json == null
-                || uploader.isShutdown()
+                || !uploader.isAcceptingJobs()
                 || !BASE64_HEURISTIC.matcher(json).find()) {
             return json;
         }