Add AdamW Optimiser

[BradyPlanden]

Feature description

Add an AdamW implementation to PyBOP. To achieve this, an implementation that matches the ask-tell interface should be completed. This optimiser will likely be the first pure PyBOP optimisation method.

Motivation

AdamW provides a weight decay implementation of the Adam algorithm. A pytorch implementation can be found here: https://pytorch.org/docs/stable/generated/torch.optim.AdamW.html

Possible implementation

No response

Additional context

No response