Impervious

Surface water balance for roof and impervious-road urban surfaces, following Oleson et al. (2010, CLM Tech Note Ch. 5) Eqs. 5.2-5.5. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:937 (`ImperviousWaterBalance` @component). Parameterized as observed-only: precipitation (q_rain, q_sno) and loss fluxes (E_surface, q_over, q_rgwl, q_snwcp_ice) are inputs; q_grnd_liq, q_grnd_ice, and water_input are algebraic outputs.