Add inverse helpers to generic calculator

[sethrj]

This is in preparation for making "views" to the optical physics data: we have at least one place where we need to "invert" a generic grid calculator.

• Complete a 'todo' for renaming Data→Record
• Refactor the "uniform grid" to directly access the underlying collection rather than storing a temporary span
• Add "from_inverse" and "make_inverse" functions to GenericCalculator