add head file to fix two build warnings (#2195)

* add head file to fix two build warnings
Signed-off-by: Nzxf <zhuxiaofeng07936@hellobike.com>

* fstream.h => fstream
Signed-off-by: Nzxf <zhuxiaofeng07936@hellobike.com>
Co-authored-by: Nzxf <zhuxiaofeng07936@hellobike.com>

core/src/index/thirdparty/hnswlib/hnswlib.h

@@ -23,6 +23,7 @@
 #endif
 #endif
 
+#include <fstream>
 #include <queue>
 #include <vector>