bug fix

[srmnitc]

This pull request introduces a conditional check for the use_composition_scaling key in the comps dictionary within the prepare_inputs_for_phase_diagram function in calphy/phase_diagram.py. If the key is not present, it defaults to True.

Key change:

• Enhancement to composition scaling logic:
  • Added a conditional check to ensure the use_composition_scaling key is explicitly handled. If the key is missing, the code now defaults use_composition_scaling to True. This improves robustness by preventing potential KeyError exceptions.