fix: Fix the problem where the  model.save_weights() can't save multi-layer weight

Add a new optimizer

fix: add EinsumGrad

fix: optimize some APIs

Add pad preprocessing for `imdb` dataset

fix: inconsistent shape error while training embedding layer

fix: A bug fix in KerasObjectLoader.cs

I added `ToArray()` so that there is no "The collection has changed" error after `_delete_tracking`.

fix: fix the bug of repeated progress bar in Model.fit()

fix: revise earlystopping callback's min_delta parameter and add GRUCell layer

feat: Add UpSampling1D layer and test.

refactor: Standardize TensorFlowNET.Keras/Losses/*

fix: type converting errors when loading imdb dataset

Improve the API of  LayerNormalization

fix: error pf training RNN on Linux

feat: Support training of RNN and LSTM.