add support for sectional dry deposition

[zdaq12]

Summary

Adds dry deposition support to the sectional representation. Also corrects the
deposition velocity formula shared by all representations to match
Zhang et al. (2001) and Emerson et al. (2020) as published.

Sectional dry deposition

scenario_binned_loss() applies per-bin loss each timestep via the same
scenario_loss_rate() dispatcher already used by the particle-resolved
and modal paths, so the sectional model supports every
loss_function_type (constant, volume, drydep, chamber), not just dry
deposition.

Each bin decays as m(t+dt) = m(t) * exp(-rate*dt) — the exact solution
of dm/dt = -rate*m. Mass (vol_conc) is
prognostic and num_conc is diagnosed, matching the convention already used by
sectional coagulation.

output_sectional()/input_sectional() gain a scenario argument so
dry deposition parameters are written to and read from NetCDF output,
mirroring output_modal()/input_modal().

Deposition velocity formula change

before: V_d = V_s + 1/(R_a + R_s + R_a*R_s*V_s)
after:  V_d = V_s + 1/(R_a + R_s)

The R_a*R_s*V_s term comes from the two-layer flux balance
(Seinfeld and Pandis, 1998); however, it is not a physically representative term, but
rather a direct artifact of the mathematical manipulation of the multilayer resistance analogy
system of equations with settling acting through all layers. Strictly speaking, neither
Zhang et al. (2001) nor Emerson et al. (2020) use this term. Both follow Slinn (1982)'s
derivation where settling is treated purely in parallel. Since drydep_params_t is explicitly
parameterized to switch between Z01-and E20 coefficient sets, retaining the cross
term would implement neither parameterization as published.

Applied in all three places: scenario_loss_rate_drydep
(particle/sectional), scenario_integrated_loss_rate_drydep (modal,
analytic), and dep_vel_integrand (modal, QUADPACK).

New spec-file option

do_aero_dilution (sectional runs) skips both background-exchange
dilution and the mixing-layer-growth correction when set to no. The
modal representation has no dilution treatment at all, so this is needed
for the modal/sectional comparison and lets dry deposition be
studied in isolation.

Tests

• test_loss_16 — sectional dry deposition regression test
• test_loss_17 — checks sectional against particle-resolved

Reference files for test_loss_13, test_loss_14 (QUADPACK), and
test_loss_16 are regenerated due to formula update.

[codecov]

Codecov Report

❌ Patch coverage is 70.76923% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.47%. Comparing base (7984020) to head (c64dddd).

Files with missing lines	Patch %	Lines
src/scenario.F90	68.75%	10 Missing ⚠️
src/run_sect.F90	72.00%	7 Missing ⚠️
src/output.F90	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
- Coverage   78.49%   78.47%   -0.03%     
==========================================
  Files          56       56              
  Lines        9755     9806      +51     
==========================================
+ Hits         7657     7695      +38     
- Misses       2098     2111      +13     

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