Aerosol interaction vn14.2

[paulfield2024]

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[paulfield2024]

This PR is linked to UM PR

Summary of changes on aerosol_interaction_vn14.2

activation.F90
dactive/dmass_d are now always initialized to zero before the ice-nucleation branch (previously only for iopt_inuc < 4), and the higher-order-scheme branch condition changed from else to explicit iopt_inuc > 3. Prevents possible use of uninitialized values for warm/low-Smax cases.

aerosol_routines.F90
aero_mact_mean_max/dust_mact_mean_max caps raised from small physical limits (~1e-15/1e-13 kg) to effectively unlimited (1e30), and most mact*_mean = min(...) clamps for secondary/tertiary categories (mact2, mact3, mact1) are commented out. Only the primary mact_mean clamp remains, but now also reduces nact/ntot (number) proportionally when the mean-mass cap is hit, rather than only capping mass.

Effect: aerosol/dust mean activated particle mass is essentially no longer artificially capped except in one place, and when it is capped, number concentration is now also adjusted to stay consistent — avoids unphysical size clamping ("bug" workaround) but changes activated-aerosol mass/number partitioning throughout activation.

mphys_tidy.F90
Adds a new "tidy" pass that zeros out several aerosol tracers (i_am1/i_an1 Aitken sol, i_am2/i_an2 Accum sol, i_am3/i_an3 Coarse sol, i_am6/i_an6 Coarse dust, i_am10/i_an10) when their mass or number falls below new aeromass_small/aeronumber_small thresholds (from thresholds module).
l_qsig/l_qsneg reset from indexing only element 0 to resetting the whole array; adds reset flags for qr, nl, ql, ni.
Fixes an index bug: an i_an12 reference in a conservation check for i_an11 corrected to i_an11.

sedimentation.F90
Aerosol/dust mass sedimentation fluxes (dmac, dmad) for cloud/rain/ice/snow/graupel categories are now capped with `min(flux, mact/(step_length*rdz_on_rho))' This limits sedimentation flux so it can't remove more aerosol/dust mass from a level than is actually present in one timestep. Applied consistently in both interior-level and boundary (top-level) flux calculations.

special.F90
casim_erfc now uses the intrinsic erfc(x) instead of erfg(x,c), noting a bug in erfg for c=1 and small x.

What it affects
Aerosol/dust activation and scavenging physics: activated aerosol mass/number partitioning across cloud, rain, ice, snow, graupel; aerosol mass conservation/tidy-up (small-value flushing); and aerosol/dust sedimentation flux stability (prevents non-physical over-removal). Also fixes a small numerical bug in the complementary error function used elsewhere in the microphysics. These changes primarily affect simulations with aerosol-cloud interaction (l_ased/dust/aerosol tracers) enabled. This should improve stability/conservation but will change aerosol-related diagnostics and activated hydrometeor mass/number.