Reduce usage of pow() and log()

[coco-yeung]

In the current version of the code running the issl_rhi140 example, around 20% of computational time is spent on the pow() function when running on 1 thread: see perf profiling below

Changes have been made to the code to reduce the reliance on pow(). The most notable changes were:

• Aerosol.cpp: implemented a switch case in the Moment functions as the power n is only ever 0, 1, 2, or 3, and saving log() results in the loop to prevent repeated calculations
• Aerosol.hpp: bypassing pow() as it is only called by LAGRIDPlumeModel.cpp where the power n is 0; it also returns the value before it is multiplied by the logBinRatio since the loop which calls it also calculates it.

Other changes made are to compute pow(x, 2) as x*x or pow(x, 1/3) as cbrt(x) instead, although I believe that made minimal difference as the compiler could already make those optimisations.

This resulted in a decrease in % time spent in the functions pow() and log(): see perf profiling below

The real time decrease for the different weather conditions are below:

<style> </style>

version	default (issl_rhi140)	shear * 1.1	rhi 120	temperature - 5	w - 0.1
main (seconds)	967	1028	1671	1157	796
feature (seconds)	710	767	1257	849	587
decrease (%)	-26.58	-25.39	-24.75	-26.62	-26.26

The changes are also zero-diff with the current main branch, verified by taking the difference between the ice mass over time and the number of ice particles at each output time.