rft: clean up precip cache computation

[haakon-e]

The treatment of various microphysical tracers is typically nearly identical. This pull request implements this abstraction by making extensive use of ClimaCores @name construct to refer to, and extract data related to, the various microphysical tracers like q_liq, q_rai, etc.

A few other significant features include:

• fusing sums over subdomains
• reducing and/or eliminating the use of cache and temporary quantities.
  • For example, ᶜwₛʲs and friends are not used at all anymore (though I haven't deleted the code that precomputes updraft sedimentation velocities just yet)
• fixes the bug identified in Bug in rain 2M+PEDMF terminal velocity calculation #4117

More details below:

---

This pull request introduces several utility functions and refactors existing code to improve clarity and maintainability in microphysics and variable manipulation modules. The main focus is on adding helper functions for terminal velocities, tracer field name conversions, and subdomain density handling. It also includes minor refactoring and documentation improvements.

Microphysics utilities:

• Added new functions in microphysics_wrappers.jl to select and compute terminal velocity functions for different microphysical schemes (1-moment and 2-moment), using the tracer name to dispatch the correct velocity calculation.

Tracer and field name utilities:

• Introduced a suite of helper functions in variable_manipulations.jl to map between grid-scale tracer names and related field names, such as get_ᶜwᵪ_name_from_qᵪ_name, get_ᶜwₙᵪ_name_from_qᵪ_name, and get_nᵪ_name_from_qᵪ_name, each with clear documentation and examples.
• Added ᶜspecific_gs_tracer to lazily compute the specific tracer field from a grid-scale tracer name, and refactored ᶜspecific_gs_tracers to use this helper for improved clarity. [1] [2]

Subdomain density handling:

• Refactored and documented the logic for computing area-weighted environment density (ρa⁰) and for accessing subdomain densities, introducing ᶜρaʲs_list and ρaʲ helpers for both prognostic and diagnostic EDMFX models.

General utilities and refactoring:

• Changed draft_sum to use unrolled_mapreduce for consistency and flexibility in summing over multiple subdomain states.
• Added a new vector abbreviation WVec in abbreviations.jl.
• Minor code cleanup and documentation improvements, including examples for new utility functions and improved docstrings. [1] [2]

These changes collectively improve the modularity, readability, and extensibility of the codebase, particularly for microphysics and tracer field management.