Add time interpolation to mpc data

[eslickj]

Fixes None

Adds option to linearly interpolate from MPC TimeSeriesData.

Summary/Motivation:

Sometimes you have time series data that doesn't line up perfectly with model time indexes. @blnicho and @jsiirola, this is part of the recent MHE work.

Changes proposed in this PR:

• Add some linear interpolation utility functions and use them to add interpolation capbility to get data and time points not in MPC TimeSeriesData

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[Robbybp]

Thanks for the addition. This is definitely functionality we were missing. I think this would be better as it's own interpolate, or get_interpolated_data, method. Would that work for your application?

There is also the question of whether to support some form of interpolation in DynamicModelInterface. (E.g., in get_data_at_time, load_data, or dedicated methods for interpolation.) I'm fine with (and think I prefer) punting for now if you don't need this for your application.

[Robbybp]

With < and > here, this will fail with a tolerance of zero (the default) if the user provides one of the endpoints. Can you update to use >= and <=?

[Robbybp]

Unless you think the endpoints should not be valid for interpolation with a tolerance of zero. I'm open to this argument.

[eslickj]

You're right should have used >= and <=. I'll fix that.