Update RO and Pump Costing Docs

[MarcusHolly]

Summary/Motivation:

The name of costing method arguments could not be found directly in the documentation. These documentation updates should probably be carried over to other unit models as well, but just adding these here as they are necessary for watertap-org/watertap_academy_fall_2025#21

Changes proposed in this PR:

• Updates RO and pump costing docs

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