rft: clean up surface code

[haakon-e]

This pull request primarily refactors and cleans up the code in the surface conditions and surface flux modules, focusing on improving readability and maintainability without changing core logic. The changes involve consolidating multi-line expressions into single lines, improving destructuring and broadcasting, and removing unnecessary variables. There are no significant algorithmic or behavioral changes.

Key refactoring and cleanup changes:

Surface conditions module (src/surface_conditions/surface_conditions.jl):

• Consolidated multi-line variable assignments and function calls into single lines throughout, improving readability [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12].
• Improved destructuring of external forcing inputs for clarity.
• Used cospi for surface temperature calculation, simplifying trigonometric expressions.
• Removed unused variables and unnecessary comments for conciseness.
• Cleaned up struct construction and field assignment for surface conditions [1] [2].

Surface state module (src/surface_conditions/surface_state.jl):

• Reformatted struct definitions and constructors to single lines for conciseness [1] [2] [3] [4].

Surface flux tendency (src/prognostic_equations/surface_flux.jl):

• Refactored calculation of total specific enthalpy for clarity and efficiency.

These changes are focused on code style and maintainability, making the codebase easier to read and modify without altering its functionality.