Add 2-hidden layer neural network with back propagation using sigmoid activation function (#4037)

* added neural network with 2 hidden layers

* Revert "added neural network with 2 hidden layers"

This reverts commit fa4e2ac86eceaae018cb18c720420665b485f3b7.

* added neural network with 2 hidden layers

* passing pre-commit requirements

* doctest completed

* added return hints

* added example

* example added

* completed doctest's

* changes made as per the review

* changes made

* changes after review

* changes

* spacing

* changed return type

* changed dtype