Show decimals for Metrics/AbcSize:Max if given in config

The reporting of the offense should include a decimal if set like that in a configuration file.

And increase the number of significant digits reported for the size. Otherwise we get output such as `[44/44]` when the size is just above 44.

Allowing a little bit of duplication makes the specs more readable than with the method `registers_offense`.

Cc @jfelchner