initial cache method removal

[kmdeck]

Purpose

Removes special methods of set_initial_cache. All models can use the default

To-do

review

Content

• bucket model method was a duplicate of the default -> easy to remove
• canopy model was a default except for set_prescribed_canopy_field call. Now we call this in update_aux and can use the default initial cache setting method.
• LSM model should have been calling update drivers, then update aux for each model, and then update boundary fluxes for each model, since this is what we do each timestep. it was instead caling update drivers, and then set initial cache for each model. Now we use the default, which does what we want.

Review checklist

I have:

• followed the codebase contribution guide: https://clima.github.io/ClimateMachine.jl/latest/Contributing/
• followed the style guide: https://clima.github.io/ClimateMachine.jl/latest/DevDocs/CodeStyle/
• followed the documentation policy: https://github.com/CliMA/policies/wiki/Documentation-Policy
• checked that this PR does not duplicate an open PR.

In the Content, I have included

• relevant unit tests, and integration tests,
• appropriate docstrings on all functions, structs, and modules, and included relevant documentation.

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• I have read and checked the items on the review checklist.

[juliasloan25]

This is a great change, thank you Kat!

[juliasloan25]

Should we keep this docstring?

[kmdeck]

I cleaned it up a bit, but I think it still holds, so keeping. let me know if you had something in mind for not including it!