Enable non-zero mu_r

[cjvogl]

Refactoring of sedimentation, evaporation, and size limiters to enable non-zero mu_r (e.g., mu_r=1 as used by EAMxx).

Tested with the following:

1. verified adiabatic case output with $\mu_r=0$ without lookup tables is within machine precision of prior result, i.e., ./rainshaft --use_zero_mur=1 from this branch vs ./rainshaft from main
2. verified adiabatic case output with $\mu_r=0$ and and lookup tables is within machine precision of prior result, i.e., ./rainshaft --use_lookup=1 --use_zero_mur=1 from this branch vs ./rainshaft --use_lookup=1 from main
3. verified adiabatic case output with $\mu_r=1$ seems reasonable, i.e., that the initial $\lambda_r$ values are scaled by $4^{1/3}$ compared to $\mu_r=0$
4. verified using numerical integration with $mu_r = 1$ results in an error message stating this is not supported

Note that machine precision here refers to an RMS difference $\approx 10^{-20}$ relative to the RMS norm of the prior solution $\approx 10^{-4}$

Here is a summary of the changes, as compiled by Claude Code, seemingly mostly from my commit messages (with me confirming the accuracy of the description):

Key Changes

Core Physics Refactoring:

• Refactored evaporation calculations to support non-zero mu_r, consolidating the Vevapi integral computation with
  proper gamma function arguments
• Updated sedimentation and rain fall speed calculations for the gamma distribution with non-zero mu_r
• Consolidated various implementations of lambda_r to consistently use mu_r from constants
• Updated size limiters to reference constants.mur consistently throughout

Configuration:

• Added mur as a configurable parameter in RainshaftConstants
• Made zero vs non-zero mu_r a CLI argument in the driver
• Added exception for numerical evaporation integration which does not support non-zero mu_r

Build System:

• Fixed CMake SUNDIALS integration to avoid unnecessary rebuilds when SUNDIALS repo is updated
• Corrected SUNDIALS CMake variable name (SUNDIALS_ENABLE_C_EXAMPLES)
• Fixed NetCDF CMake module to explicitly link HDF5 target, preserving HDF5 paths