Implement longwave radiation diagnostics

@zmaalick is already working on this.

Since Aug 13, 2026.

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

Implement the following diagnostics:

Diagnostic 1:
CF Standard name: surface_upwelling_longwave_flux_in_air
long name: Surface Upwelling Longwave Radiation
Unit: W m-2
Region: global
Time operation: time mean
Stash expression: m01s02i207[lbproc=128] - m01s02i201[lbproc=128] + m01s03i332[lbproc=128] - m01s02i205[lbproc=128]
Additional description: It may requires available ids radiation__lw_down_surf_rts, radiation__lw_net_surf_rts, radiation__lw_up_toa, radiation__lw_up_toa_rts

Diagnostic 2:
CF Standard name: surface_upwelling_longwave_flux_in_air
long name: Surface Upwelling Longwave Radiation
Unit: W m-2
Region: global
Time operation: Instantaneous
Stash expression: m01s02i207[lbproc=0] - m01s02i201[lbproc=0]
Additional description: may Requires available ids radiation__lw_down_surf_rts, radiation__lw_net_surf_rts

Diagnostic 3:
CF Standard name: surface_upwelling_longwave_flux_assuming_clear_sky
long name: Surface Upwelling Clear-Sky Longwave Radiation
Unit: W m-2
Region: global
Time operation: time mean
Stash expression: m01s02i219[lblev=1, lbproc=128] + m01s03i332[lbproc=128] - m01s02i205[lbproc=128]
Additional description: May Requires available ids radiation__lw_up_clear_rts, radiation__lw_up_toa, radiation__lw_up_toa_rts

Diagnostic 4:
CF Standard name: surface_net_downward_longwave_flux
long name: Net Longwave Surface Radiation
Unit: W m-2
Region: global
Time operation: time mean
Stash expression: m01s02i201[lbproc=128] - (m01s03i332[lbproc=128] - m01s02i205[lbproc=128])
Additional description: Requires available ids radiation__lw_net_surf_rts, radiation__lw_up_toa, radiation__lw_up_toa_rts

Diagnostic 5:
CF Standard name: toa_outgoing_longwave_flux_assuming_clear_sky
long name: TOA Outgoing Clear-Sky Longwave Radiation
Unit: W m-2
Region: global
Time operation: time mean
Stash expression: m01s02i206[lbproc=128] + m01s03i332[lbproc=128] - m01s02i205[lbproc=128]
Additional description: May requires available ids radiation__lw_up_clear_toa_rts, radiation__lw_up_toa, radiation__lw_up_toa_rts

Diagnostic 6:
CF Standard name: surface_upwelling_shortwave_flux_in_air
long name: Surface Upwelling Shortwave Radiation
Unit: W m-2
Region: global
Time operation: time mean
Stash expression: m01s01i235[lbproc=128] - m01s01i201[lbproc=128]
Additional description: May Requires available ids radiation__sw_down_surf_rts, radiation__sw_net_surf_rts

Diagnostic 7:
CF Standard name: surface_upwelling_shortwave_flux_in_air
long name: Surface Upwelling Shortwave Radiation
Unit: W m-2
Region: global
Time operation: Instantaneous
Stash expression: m01s01i235[lbproc=0] - m01s01i201[lbproc=0]
Additional description: May Requires available ids radiation__sw_down_surf_rts, radiation__sw_net_surf_rts

Diagnostic 8:
CF Standard name: toa_outgoing_longwave_flux_assuming_clear_sky
long name: TOA Outgoing Clear-Sky Longwave Radiation
Unit: W m-2
Region: global
Time operation: Instantaneous
Stash expression: m01s02i206[lbproc=0]
Additional description: From Port for proto-GAL

### Further details of the issue.

_No response_