fix(process): scale LiquidRemover mass rate by gas mass fraction

[olelod]

Type of Work

• Patch: X.Y.Z+1. NEGLIGIBLE visible changes, does not change input or output - OR changes behaviour. Use chore:, refactor: etc
• Minor: X.Y+1.Z. Minor changes, might ADD new input (YAML), or other backwards-compatible changes. Use feat:, fix:
• Major: X+1.Y.Z. Major and most likely BREAKING changes, wo. backwards compatibility, or removing temporary backwards compatibility functionality. Use ! or BREAKING:.

See here (internal): https://github.com/equinor/ecalc-internal/discussions/1044

Have you remembered and considered?

• IF FEAT: I have remembered to update documentation
• IF FIX OR FEAT: I have remembered to update manual changelog (docs/drafts/next.draft.md)
• IF BREAKING: I have remembered to update migration guide (docs/docs/migration_guides/)
• IF BREAKING: I have committed with BREAKING: in footer or ! in header
• I have added tests (if not, comment why)
• I have used conventional commits syntax (if you squash, make sure that conventional commit is used)
• I have included the Github issue nr in the footer!

What is this PR all about?

When LiquidRemover activates on a two-phase inlet, it removes the liquid phase from the composition but previously kept the total mass rate unchanged — so the dropped-out liquid mass was effectively re-injected into the gas stream downstream.

This PR scales the outlet mass rate by the gas mass fraction so the removed liquid is no longer carried by the gas:

gas_mass_fraction = vapor_fraction_molar * outlet_molar_mass / inlet_molar_mass
new_mass_rate     = inlet.mass_rate * gas_mass_fraction

Pure-vapor inlets are unchanged.

What else did you consider?

Also exposing the removed liquid as a separate outlet stream (e.g. for routing to an oil pump or emissions accounting). Left as a docstring note — it would change propagate_stream's contract and there is no consumer for it yet.

Between the lines?

Resolves equinor/ecalc-internal#1767

[tj098895]

looks good. leaves it for @kjbrak to reverify

[kjbrak]

Consider failing explicitly when inlet_molar_mass <= 0.0 rather than preserving the full inlet mass rate. A non-positive molar mass is non-physical, and gas_mass_fraction = 1.0 would hide the invalid thermodynamic state while carrying all removed-liquid mass downstream again for that edge case.

If using InvalidStreamException, the matching import also needs to be added.

Suggested change

	if inlet_molar_mass > 0.0:
	gas_mass_fraction = inlet_stream.vapor_fraction_molar * new_fluid.molar_mass / inlet_molar_mass
	else:
	gas_mass_fraction = 1.0
	if inlet_molar_mass <= 0.0:
	raise InvalidStreamException(
	f"Cannot remove liquid from stream with non-positive molar mass: {inlet_molar_mass}"
	)
	gas_mass_fraction = inlet_stream.vapor_fraction_molar * new_fluid.molar_mass / inlet_molar_mass