Refactoring

[reubenharry]

I wrote a few refactors, to remove a bit of code.

I don't know if this will break anything on @JakobRobnik 's ensemble branch, so you should probably try merging it in, and checking.

Main changes:

1. output == "normal" -> output == OutputType.normal: this way you don't pass in arbitrary strings as arguments. The possible options are given by OutputType = Enum('Output', ['normal', 'detailed', 'expectation', 'ess'])
2. Instead of passing in 'MN' or 'LF', directly pass in the integrator function. This meant I could remove hamiltonian entirely.
3. if ... else replaced in some places by case, e.g.

match output:
            case OutputType.normal:
                X, _, E = self.sample_normal(num_steps, x, u, l, g, key, L, eps, sigma, thinning)
                return X
            case OutputType.detailed:
                X, _, E = self.sample_normal(num_steps, x, u, l, g, key, L, eps, sigma, thinning)
                return X, E, L, eps
...