Implement recurrent layers

[ricor07]

Particularly, RNN, SimpleRNN, LSTM, and GRU.

[milancurcic]

There is a WIP basic RNN PR here: #162

Not sure how much it's reusable, or its current state, @castelao may chime in.

[ricor07]

Do you mind if I start working on @castelao 's fork? Of course he will be cited

[castelao]

Hi everyone. I'm sorry for the slow response and thanks for checking.

I had the RNN working back in 2023 and did use it, but I don't remember anymore why we didn't conclude and merged that. I think that main received some changes and diverged from my fork and I didn't have the chance to conform. I would be excited to see RNN implemented in main, even better with LSTM and all the other variations. If what I did is helpful, please take it and move it forward, otherwise, fell free to close that branch and do it on your way. Whatever @milancurcic thinks is the most efficient and better way to move forward, works for me.

Tomorrow evening I'll look in my archives to remind myself what I did and update #162 with what I find.

[milancurcic]

Thanks @castelao, no worries. The main reason why I didn't push it to conclusion yet was because it remained marked as draft so I thought the design was still changing. Getting that PR up to speed should be easy (and I can do it too, if needed). Just mark it as ready for review if you think it is.