Improve resistor-color-duo: map to math #51

Describe the improvement:

When an optimal map solution is provided, the analyzer should approve but provide a comment that allows them to continue the path.

Perhaps there is a solution that does not involve type-juggling: the act of creating a 
_string_ of numbers (the digits) and then parsing it back into a number. For example: 
what _value_ does the `4` in the number `42` hold.

You may continue with the next exercise, or try out submitting a more math-y solution 
and continue here.

Which exercise

resistor-color-duo

Additional context

The ResistorColorDuoAnalyzer has a method that checks if an exercise is optimal. There are various ways to branch based on that optimality. As per the commentary above, using a map is approvable but not optimal.

• ResistorColorDuoSolution::Entry#isOptimal
• ResistorColorDuoAnalyzer#checkForTips