Simple optimizers

This section explores how to implement a small module of optimization algorithms in Rust.

We begin by defining a common interface for optimizers and show how different strategies like gradient descent and momentum-based methods can be implemented using Rust's trait system.

Then, we explore an alternative design using enums, which can be helpful when working with simpler control flow or dynamic dispatch.

Finally, we demonstrate how to replace Vec<f64> with ndarray structures, which allows for more expressive and efficient numerical code, especially for larger-scale or matrix-based computations.

The goal is to gradually expose the design space for writing numerical algorithms idiomatically in Rust.