Unit handling

Need to add better unit handling across all widgets.

CD Titration Calculator:
- need unit on volumes/concentrations

Processing:
- Can we read wavelength units from file?

Delta epsilon:
- concentration/MW

Binding Plot:
- orders of magnitude required to make sure results are correct units

can we use Pint across widgets to ensure this is all correct?

Start by reading the CD Titration Calculator, Processing, Delta epsilon, and Binding Plot widget entry points to map their current volume, concentration, wavelength, molecular-weight, and order-of-magnitude handling. Check how units enter from files and user inputs, then define consistent unit behavior across all widgets and verify that calculated results retain correct units.

Written by the indexing model from the issue text.