update building radiation utils for external radiative heat transfer

[ecosang]

Adding several external radiative heat transfer-related utils.

New functions in building_radiation_utils.py:

• _ensure_irradiance_components() — Normalizes irradiance input (dict or dataclass) to a guaranteed IrradianceComponents instance with validation of required keys (ghi, dni, dhi, solar_zenith, solar_azimuth)

• validate_fenestration_connectivity() — Validates that fenestration nodes in a floor plan properly bridge exterior space to interior air (checks air adjacency, exterior exposure, surrounded-by-air detection, and chain connectivity)

• _validate_fenestration_chain_connectivity() — Ensures each fenestration node can reach both exterior and interior air through the fenestration chain via BFS, and validates interior-facing direction is not blocked

• _determine_interior_direction() — Infers the direction vector pointing from exterior toward interior air based on node positions relative to grid boundaries or adjacent exterior space

• _find_connected_groups() — Finds all 4-connected groups of cells with a given value in the floor plan using BFS

• mark_fenestration_positions() — Classifies fenestration nodes into exterior, interior, or in-between categories based on adjacency

• group_fenestrations() — Groups adjacent fenestration nodes and computes surface properties (azimuth, tilt, view factors F_sky/F_gnd/F_air, beta)

• _determine_fenestration_azimuth() — Determines fenestration azimuth from exterior adjacency using atan2, with floor_plan_orientation offset support

• group_air_nodes() — Groups connected interior air nodes and annotates which fenestration groups are adjacent to each air group

• calculate_solar_absorbed_for_fenestration_group() — Computes absorbed solar flux per node for a fenestration group using POA irradiance

• net_solar_absorbed_heatflux_fenestration() — Returns array of absorbed solar heat flux at each fenestration node across all groups

• calculate_solar_transmitted_for_fenestration_group() — Computes total transmitted solar radiation for a fenestration group

• net_solar_transmitted_heatflux_fenestration() — Distributes transmitted solar heat flux to air nodes connected to windows

• mark_interior_surface_adjacent_to_air() — Marks interior surfaces (walls + fenestration) adjacent to air with boolean mask

• calculate_exterior_lwr_for_fenestration_group() — Computes net exterior longwave radiative heat flux for a fenestration group (sky + ground + air exchange)

• net_exterior_radiative_heatflux() — Computes net exterior LWR heat flux array for all fenestration nodes

• get_exterior_wall_boundary_mask() — Identifies exterior wall nodes forming the building boundary (excluding walls facing enclosed interior air)

• determine_exterior_wall_azimuth_array() — Determines azimuth for each exterior wall boundary node based on adjacent exterior space direction

New tests in building_radiation_utils_test.py:

• 6 dedicated unit tests for _validate_fenestration_chain_connectivity() — Testing valid chains, blocked-from-exterior, blocked-from-air, interior-direction blockage, thick fenestration, and L-shaped fenestration
• new tests for the above added functions.

Code cleanup:

• Removed unused interior_wall_value parameter from _validate_fenestration_chain_connectivity() and all callers

[ecosang]

@s2t2
Several building radiation utility functions are added.
We may want to have a single class to handle all radiative heat transfer, but I only use those functions within the current simulator/building framework, so I think this structure is ok to maintain.
It can be debugged while testing simulator for other developers.

[s2t2]

Nice @ecosang , thank you! There is a lot of code - I will work on reviewing by later this week / early next week.