Call fsync after appending to history file

This is an attempt to eliminate history file corruption as described in
https://github.com/fish-shell/fish-shell/issues/10300.
In particular, issues raised in
https://github.com/fish-shell/fish-shell/issues/10300#issuecomment-2567063654
can benefit from such synchronization.

src/history.rs

@@ -48,6 +48,7 @@
     expand::{expand_one, ExpandFlags},
     fds::wopen_cloexec,
     flog::{FLOG, FLOGF},
+    fs::fsync,
     history::file::{append_history_item_to_buffer, HistoryFileContents},
     io::IoStreams,
     operation_context::{OperationContext, EXPANSION_LIMIT_BACKGROUND},
@@ -696,6 +697,7 @@ fn save_internal_via_appending(&mut self, history_path: &wstr) -> std::io::Resul
         }
 
         flush_to_file(&mut buffer, locked_history_file.get_mut(), 0)?;
+        fsync(locked_history_file.get())?;
         self.first_unwritten_new_item_index = new_first_index;
 
         // Since we just modified the file, update our history_file_id to match its current state