use `LandSimulations` struct for Fluxnet simulations

[juliasloan25]

We have a struct ClimaLand.Simulations.LandSimulations which is being used in global longruns. We should also use it for fluxnet simulations to make running site-level and global simulations more similar.

Note: the existing LandSimulations constructor sets initial conditions by calling make_set_initial_state_from_file. This may work for site-level runs but it would be better to use fluxnet data for ICs with the function set_fluxnet_ic!. We should unify the interface for these two functions, and call the correct one based on the simulation type (fluxnet vs global).

[imreddyTeja]

This will probably be done along with issue #1190 , but I could also not convert the fluxnet simulations. They don't need anything special to use LandSimulation other than not using the default set_ic!, and a slight adjustment to the plotting/results checks to reflect the changed ordering of callbacks.

[kmdeck]

I believe this is closed by #1190 and #1288