fix: make buffering optional per variable

apps/hiopy/_data_handler.py

@@ -20,7 +20,9 @@ class DataHandler:
             dim: chunk_size for dim, chunk_size in zip(var.attrs["_ARRAY_DIMENSIONS"], var.chunks)
         }
         self.time_chunk_size = chunks["time"]
-        self.buf = np.empty([self.time_chunk_size, *var.shape[1:-1], ma - mi], dtype=var.dtype)
+        self.use_buffer = var.attrs.get("hiopy::use_buffer", self.time_chunk_size > 1)
+        if self.use_buffer:
+            self.buf = np.empty([self.time_chunk_size, *var.shape[1:-1], ma - mi], dtype=var.dtype)
 
     def flush(self):
         if self.prune_offset is not None:
@@ -38,12 +40,15 @@ class DataHandler:
             self.loco_server.set_timestep(self.var.name, self.t - 1)
 
     def __call__(self, event):
-        self.buf[self.t % self.time_chunk_size, ...] = np.transpose(event.data)
         logging.info(
             f"received {self.var.name} at {self.t % self.time_chunk_size+1}/{self.time_chunk_size}"
         )
+        if self.use_buffer:
+            self.buf[self.t % self.time_chunk_size, ...] = np.transpose(event.data)
+        else:
+            self.buf = np.transpose(event.data)
         self.t += 1
-        if self.t % self.time_chunk_size == 0:  # chunk complete
+        if self.t % self.time_chunk_size == 0 or not self.use_buffer:  # chunk complete
             self.flush()
 
     def set_loco_server(self, loco_server):