bug(code): the SQL visualizer doesn't differentiate between ints and floats

[itsvs]

In SQL, 3/2 and 3.0/2 are treated differently, but since the code.cs61a.org SQL interpreter is written in JS, this functionality isn't properly reflected in the step-by-step visualizer. The fix here is to wrap all values in a JS object that includes their type, and to write logic around this type. This fix is a bit too involved to be implemented this close to the SU21 final, as things might break if something goes wrong, but it should be fixed soon after.