[feature] Create simple nearest neighbour sampler

[b-barton]

Is your feature request related to a problem?

We need a sampler we can start using and building around.

Describe the solution you'd like...

1. Flesh out a nearest neighbor sampler for identifying and extracting grid points based on a given set of time, latitude, longitude coordinates following the sampler template.
2. Test it behaves as expected.

Describe any alternatives you've considered...

No response

Additional context

No response

[b-barton]

I've coded up a sampler that finds the nearest neighbour using latitude and longitude. I've used argsort here so it could be expanded later to do a horizontal interpolation of the nearest points.

The tests cover a single profile on a model gridpoint, multiple profiles and profiles that are not on a model grid point. I the future we can add behavior for profiles on or near land.