Make `numeric` columns return a number instead of a string when possible

[Marc-Andre-Rivet]

Relates to #166 and to #297 specifically.

As currently implemented the table's numeric columns return a string when edited instead of a number. When capable of doing so the numeric type should return a number instead of expecting the on_change layer to handle the coercion.

As is, it is not possible to use on_change: { action: 'validate' } for these columns as the value is always a string.