fix(numberFilter): numbers rounding to zero shouldn't be negative

@lgalfaso here is a little PR for the numberFilter that doesn't aim at changing the current code structure. My goal here was to share tests that I've added while looking at this filter code. IMO it would be good to get them in before doing bigger refactorings on this filter.

As a side effect this PR fixes inconsistency in formatting numbers that round to zero.

Once again, I'm not trying to clean up the whole code here but do minimal changes that fixes inconsistencies and bring in more tests. For me the value of this PR is in tests.