Validation does not check column types

[Pennycook]

Expected behavior

We should either:

• Check that columns which we expect to be numeric (like fom) are actually numeric, and raise an exception if the condition does not hold; or
• Try to cast columns which we expect to be numeric to numeric (with to_numeric) and raise an exception if the conversion fails.

Actual behavior

Loading data from an outside source (like JSON) that stores FOM information as strings can lead to strange results, because:

• The maximum FOM is determined by its position in a lexicographic order.
• Efficiency is calculated relative to this FOM, resulting in efficiencies outside of [0, 1].

Steps to reproduce the problem

Use string representations of the FOM instead of numeric ones.

Specifications

Tested with the tip of main.

[Pennycook]

After some more investigation, it's now clear that we validate that columns are convertible to numeric values (with _require_numeric) but don't actually perform the conversion.