Interpolation in Track-to-Track associators and metrics.

[sdhiscocks]

A few times a use case has come up to use Stone Soup metrics to investigate existing track and truth data sets, but this can be difficult if the track/truth timestamps do not align, as then states on the track/truth cannot be compared. It would be good if the data associators (and then in turn metrics?) supported interpolating tracks/truths. It may also be better if this was a separate pre-process to using associators/metrics?

I think it would make sense to look at the smoother components in Stone Soup to help with interpolation.