Replace .ToArray() with .ToList() to allow dynamic modification of network_nodes in MapGraphNetwork()

Replaced .ToArray() with .ToList() to resolve the issue where .Add() was called on a fixed-size array.

This preventing the "Collection was of a fixed size" error when called something like this var model = keras.Model(new Tensors(new Tensor[] { encoder_inputs, decoder_inputs }), outputs: decoder_dense);

fix: Resolve fixed-size array issue