Topmodel: Fix unit conversion errors in BMI calculation

[mkarim-rtx]

https://jira.nextgenwaterprediction.com/browse/NGWPC-10685

Issue

TOPMODEL exposes land_surface_water__baseflow_volume_flux in units of: m h-1 while NWM expects: m3/s

This caused NGEN unit conversion warnings: Unable to convert m h-1 to m3/s

Fix

A new BMI output variable was added: land_surface_water__baseflow_volume_flux_m3_per_s

The original variable remains unchanged: land_surface_water__baseflow_volume_flux → m h-1

The new NWM-facing variable converts TOPMODEL baseflow depth-rate into discharge:

qb_m3_per_s = qb * catchment_area / 3600

Where:

qb = baseflow rate in m h-1
catchment_area = catchment area in m2
3600 converts hours → seconds

Why
Preserves native TOPMODEL output semantics
Avoids changing existing BMI variables
Provides an NWM-compatible discharge output
Maintains consistency with fixes applied to other hydrologic modules

Result
Eliminates unit conversion warnings
Provides correct NWM-facing baseflow discharge output
Maintains backward compatibility for existing workflows

[jswade-rtx]

I tested Mohammed's Topmodel branch unit_conversion_mohammed with msw-mgr branch jwade_NGWPC-10695_output_units and successfully ran an NWM Output Variable run for a Topmodel formulation to produce the new land_surface_water_baseflow_volume_flux_m3_per_s variable.