Update the interface for calling fluid properties in coolant_values file

The current coolant values file calls the fluid properties in an inefficient way based on the old old matlab file. Needs to be more like fuel_props in the future. This would be something for a future project.

Start by comparing the coolant_values file with fuel_props and the old MATLAB file to understand the current fluid-property calls. Determine the intended interface and how completion should be verified; the issue does not name specific paths, tests, or a settled target.

Written by the indexing model from the issue text.