Grokfast exponential moving average Optimizer

### Motivation and description

Algorithm 2 in https://arxiv.org/pdf/2405.20233 should be a very easy implementation

### Possible Implementation

_No response_

Start by reading Algorithm 2 in the linked paper and comparing its update rule with the existing optimizer entry points in Optimisers.jl. Confirm the implementation matches the paper and integrates with the repository's learning-loop usage; the issue does not name a file or test, so those locations must be identified first.

Written by the indexing model from the issue text.