[fix](split) remove retry when fetch split batch failed (#37636)

## Proposed changes

We need to remove the retry logic for failed to fetch split batch.
Originally, this was implemented to handle cases where the cached client
connection might have been lost and needed to be reestablished. However,
this retry mechanism can lead to data loss. For instance, if a batch of
data has already been sent, retrying can cause this batch to be lost
without the receiver being aware of it.

be/src/vec/exec/scan/split_source_connector.cpp

@@ -56,14 +56,8 @@ Status RemoteSplitSourceConnector::get_next(bool* has_next, TFileRangeDesc* rang
         TFetchSplitBatchResult result;
         try {
             coord->fetchSplitBatch(result, request);
-        } catch (std::exception& e1) {
-            LOG(WARNING) << "Failed to get batch of split source: {}, try to reopen" << e1.what();
-            RETURN_IF_ERROR(coord.reopen());
-            try {
-                coord->fetchSplitBatch(result, request);
-            } catch (std::exception& e2) {
-                return Status::IOError("Failed to get batch of split source: {}", e2.what());
-            }
+        } catch (std::exception& e) {
+            return Status::IOError<false>("Failed to get batch of split source: {}", e.what());
         }
         _last_batch = result.splits.empty();
         _scan_ranges = result.splits;

fe/fe-core/src/main/java/org/apache/doris/datasource/SplitSourceManager.java

@@ -61,7 +61,12 @@ public void removeSplitSource(long uniqueId) {
     }
 
     public SplitSource getSplitSource(long uniqueId) {
-        return splits.get(uniqueId).get();
+        WeakReference<SplitSource> ref = splits.get(uniqueId);
+        if (ref == null) {
+            return null;
+        } else {
+            return ref.get();
+        }
     }
 
     @Override