Writing data to file

https://github.com/chenziao/Stylized-Cell-Inference/blob/f9be33417a06fa27ed97b1501b310989f988771c/stylized_module/base/active_model_synapse_input.py#L268

- Move the "writing to file" part to a separate function in the class and keep "get_lfp" as it was. In that function, specify the argument index in get_lfp(index) with the n cells (just range(self.n)) under current node.

- Writes to separate temporary files.

- Do not concatenate id with lfp in the array, since they are not of the same data type. Can create a separate dataset, e.g. called ids, in the same h5 file, just for storing the ids.