Refactor boundary flux/value methods (again)

See merge request sparcs/cryogrid/cryogridjulia!54

Improve prognostic variable initialization and refactor soil parameterization

See merge request sparcs/cryogrid/cryogridjulia!53

Also includes some minor reorganization of module files.

Improve and generalize boundary damping scheme

See merge request sparcs/cryogrid/cryogridjulia!52

Add snow damping effect for Dirichlet temperature forcings

See merge request sparcs/cryogrid/cryogridjulia!50

Refactor state handling and model builder

See merge request sparcs/cryogrid/cryogridjulia!49

This is a complete overhaul of the internal state handling system in `LandModel`.

The main goal was to decouple discretized ("on grid") state variables from the stratigraphy.

Grid variables are now stored and handled separately, allowing for more flexibility in modifying the stratigraphy mid-simulation.

Most notably, layer boundaries are now fully treated as parameters which can be tuned without rebuilding/recompiling the model.

While dynamic grid/stratigraphies are still not directly supported, this new state system provides a better basis for providing this functionality in the future.

Refactor module naming and organization

See merge request sparcs/cryogrid/cryogridjulia!48

- Move CryoGridOutput to IO module (makes more sense).
- Move CryoGridProblem and related code to new Drivers module.
- Rename Processes module -> Physics
- Rename Setup module -> Land
- Rename CryoGridSetup -> LandModel

Fix DallAmico freeze curve gradient issue

See merge request sparcs/cryogrid/cryogridjulia!47

Refactor parameter and state handling system

See merge request sparcs/cryogrid/cryogridjulia!46