[feature request] enable parallelization for ermsfkit

[marinegor]

Is your feature request related to a problem?

Would be nice to have parallelization enabled, as described here: https://docs.mdanalysis.org/stable/documentation_pages/analysis/parallelization.html

Describe the solution you'd like

I think just adding

def _get_aggregator(self):
    return ResultsGroup(lookup={"ermsf": ResultsGroup.ndarray_vstack}) # or hstack

@classmethod
def get_supported_backends(cls):
    return (
        "serial",
        "multiprocessing",
        "dask",
    )

_analysis_algorithm_is_parallelizable = True

would be enough, but unfortunately I'm not familiar with how results should look like to properly check that