Fix input sky unit error

[mj-gomes]

This PR fixes #548

origin_unit in _get_cmb_unit_conversion() is by default K_CMB, but then when calling pysm3.bandpass_unit_conversion we do not specify that as the input unit, so it was using the default uK_RJ.

Now it is working.

TODO before merging: (DONE)

• Fix expected values in tests

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
litebird_sim
input_sky.py
mpi.py
observations.py
simulations.py
litebird_sim/mapmaking
common.py
destriper.py
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[mj-gomes]

Added a CI test for the verification of correct conversion when bandpass integrating.

[mj-gomes]

I noticed something which can be improved for tidiness. Currently, we assume the input cmb power spectrum used to generate the cmb map is always in uK_CMB (see here), and then we apply the scaling factor so that our base units are K_CMB. We then perform conversions from that on, and that is coherent with the default unit in here being K_CMB.

For this reason, the following part of the cmb unit conversion code is never reached:

litebird_sim/litebird_sim/input_sky.py

Lines 109 to 118 in 7e16832

	# If origin is not K_CMB, we calculate the factor for the origin unit
	# and take the ratio.
	# Value_Target = Value_K_CMB * C_target
	# Value_Origin = Value_K_CMB * C_origin => Value_K_CMB = Value_Origin / C_origin
	# Value_Target = (Value_Origin / C_origin) * C_target
	# Factor = C_target / C_origin
	factor_to_origin = pysm3.bandpass_unit_conversion(
	freqs, weights, origin_astropy
	)
	return (factor_to_target / factor_to_origin).value

We should either delete this part, or relax the assumption that the input power spectrum is always in uK_CMB (and in that case add a parameter to SkyGenerator stating the unit of the input spectrum in case one is given).

What do you think? I suppose we always use uK_CMB, so I don't know if the second option is relevant, but in that case we can just delete the code.