refactor(score): normalize distance map values

[donhardman]

• Add normalizeMapValues to Arrays utility
• Use normalized values for distance scoring
• Preserve string keys during normalization

[donhardman]

The intent is to get rid of the PHP bug while utilizing Ds\Map instead of buggy arrays.

Example of the issue:

$ php -r '$a = "3"; $b[(string)$a] = 1; var_dump($b);'

array(1) {
  [3]=>
  int(1)
}