check that the opacity from MCFOST matches that expected from the nucleation arrays in phantom

[danieljprice]

We should perform an internal consistency check that the opacity computed from the reconstructed grain size distribution from the nucleation arrays in phantom gives the same opacity as would be expected from the third moment (K_3) as used in Siess+2022. This should be true in the small grain limit (a << lambda) for amorphous carbon grains.

[cpinte]

We also need to check the normalisation of the dust mass.
On light_17600, I get Dust mass in phantom dump is 2.2994207E-05 Msun