Implement rnn in torch backend

[chenmoneygithub]

For reference, contributors can look at:

• tensorflow rnn: link
• Jax rnn: link

The rnn part is necessary, gru and lstm could be a followup.

To test the implementation works, please use the layer tests, e.g.,

pytest keras_core/layers/rnn_test.py

[nkovela1]

@chenmoneygithub I can take torch RNN. Working on other bugs now and will pivot to this afterwards!