Adds a new SampledCoordinate coordinate type with fixed sampling interval.

This coordinate types is more similar to what used in seismology: one unique sampling rate, several starts associated with number of continuous points.

| S1 - - - - - - - | S2 - - - - | S3 - - - - - - - - - - - - |
         N1              N2                    N3
Delta = -

This new coordinate type is closer to the original data layout, have a better defined unique sampling interval but does not natively deals with gaps and overlaps. Those are determined a posteriori using a given tolerance.

This PR make some important refactoring of the Coordinate part by making defining a clearer API that every coordinate type must follow

InterpCoordinated is still the default for now, but the user can chose to try this coordinate system by using the ctype kwarg:

xd.open_dataarray("path", engine="format", ctype={"time": "sampled", "distance": interpolated"})

TODO:

• Code
• Tests
• Docs
• Release note entry