[fix](multi table) fix single stream multi table memory leak (#38255)

We meet OOM when using single stream multi table

![image](https://github.com/user-attachments/assets/748e9914-d591-4f41-8b28-412d3cecc841)

It exist memory leak, and heap profile like:

![image](https://github.com/user-attachments/assets/af30c593-88ea-44f6-bba1-82436b13f99f)

The stream load context will not release in some exception conditions as
plan failed for high concurrency causing timeout when obtaining read
lock. It is introduced by #35458

The solution effect is shown in the following figure, which can run
stably with a small amount of memory

![image](https://github.com/user-attachments/assets/4483e0a5-6c0c-4cdc-b8ed-3408da6a86b2)

be/src/io/fs/multi_table_pipe.cpp

@@ -326,6 +326,19 @@ void MultiTablePipe::_handle_consumer_finished() {
     _ctx->number_filtered_rows = _number_filtered_rows;
     _ctx->number_unselected_rows = _number_unselected_rows;
     _ctx->commit_infos = _tablet_commit_infos;
+
+    // remove ctx to avoid memory leak.
+    for (const auto& pair : _planned_tables) {
+        if (pair.second) {
+            doris::ExecEnv::GetInstance()->new_load_stream_mgr()->remove(pair.second->id);
+        }
+    }
+    for (const auto& pair : _unplanned_tables) {
+        if (pair.second) {
+            doris::ExecEnv::GetInstance()->new_load_stream_mgr()->remove(pair.second->id);
+        }
+    }
+
     LOG(INFO) << "all plan for multi-table load complete. number_total_rows="
               << _ctx->number_total_rows << " number_loaded_rows=" << _ctx->number_loaded_rows
               << " number_filtered_rows=" << _ctx->number_filtered_rows