Update hyperparameters, .gitignore, and WaveRNN training notebook

Update default checkpoint name in WaveRNNConfig for consistency

Add WaveRNN dataset class and update hyperparameters for training

Refactor dataset path handling in hyperparams and model; update .gitignore to include environment files

Update dataset path in hyperparams and model; add training test script

Add support for Arabic characters in Tokenizer and update imports