sdk/rust: Fix pwrite not flushing buffer before returning

The pwrite implementation was not flushing the file buffer before
returning, which could cause data loss since write_all only writes
to Tokio's internal buffer. Callers expect data to be persisted
when pwrite returns successfully.

Author: penberg

sdk/rust/src/filesystem/hostfs.rs

@@ -131,6 +131,7 @@ impl FileSystem for HostFS {
 
         file.seek(std::io::SeekFrom::Start(offset)).await?;
         file.write_all(data).await?;
+        file.flush().await?;
         Ok(())
     }