Allow `model_tides` to work for one timestep per one point

[robbibt]

Currently model_tides automatically runs multiple timesteps for each tide modelling lat/lon point. This serves our main DEA use case: predicting tides at set tide modelling locations for every timestep in a satellite timeseries. This is effectively:

• One point, many timesteps

However, another common use case is to model tide heights where each lat/lon point has a unique timestep. E.g.:

• One point, one timestep

We should also support this second use case, perhaps by adding a new "mode" param:

• "one-to-many"
• "one-to-one"

[robbibt]

Closed by #1142